CORNELL 
 
 UNIVERSITY 
 
 LIBRARY 
 
 ENGINEERING LIBRARY 
 
QE 361.886"""""'™"'""-"'"^^ 
 
 '^iNiiiiii'iMmif'^* mineral gallery of the Br 
 
 3 1924 004 094 748 
 
Cornell University 
 Library 
 
 The original of this book is in 
 the Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924004094748 
 
A GUIDE 
 
 MINERAL GALLERY 
 
 or THE 
 
 BRITISH MUSEUIVI (NATURAL HISTORY), 
 
 CROMWELL ROAD, SOUTH KENSINGTON. 
 
 WITH AN" INTEODUCTION 
 
 TO 
 
 THE STUDY OF MINEEALS. 
 
 FEINTED BY OEDEE OP THE TEUSTEES. 
 1885. 
 
LONDON; 
 FEINTED BY WILLIAM CLOWES AND SONS, Limited, 
 
 STAUPOED STBEET AHD CHABmc CBOSS. 
 
MINERAL G-ALLERY. 
 
 It is recommended that the Collections be studied in the 
 following order : 
 
 I. The Intboduction to the Study of Minerals, in the 
 first window-case on the left-hand side of the Gallery (pages 
 17-60). 
 
 II. The Chabactees of Mineeals, illustrated in the three 
 succeeding window-cases (pages 61-69). 
 
 III. The Species and Varieties of Minerals, in the 
 forty-two table-cases of the Gallery (pages 73-113). 
 
 IV. The Intboduction to the Study of Meteorites, 
 in the Pavilion at the end of the Gallery (see the special 
 Guide). 
 
 V. The Crystals, Models of Crystals, and Pseudo- 
 MOBPHS, in fifteen of the remaining window-cases (pages 
 70-72). 
 
 VI. The Rocks, in the wall-cases. 
 
 To find the position in the Gallery of any of the more 
 common and interesting minerals, the visitor should refer to the 
 Index (page 116), where references are given to the table-case in 
 which specimens of the mineral are placed, and to the page 
 upon which the mineral is mentioned in the Guide. 
 
 For the use of the student there is published a separate and 
 complete Index to the names and synonyms of all the mineral 
 species and varieties represented in the Collection. 
 
 a 2 
 
PREFACE. 
 
 Every visitor to a Natural History Museum cau trace a 
 likeness between the Animals and Plants shown there and those 
 with which he is already familiar, and he is thus ready to derive 
 pleasure and instruction from their examination. 
 
 But when he comes to the Minerals, and finds that with life 
 and organised structure has apparently disappeared everything 
 which gives separateness to the individual, and that hardly any 
 distinctive character seems to be left save colour, he becomes 
 impressed with the idea that, while their beauty is evident, 
 minerals must fail of being discriminated unless we penetrate 
 beyond their superficial aspects. 
 
 An attempt is made in the present Guide to facilitate the 
 comprehension of the subject by " An Introduction to the Study 
 of Minerals." It is there sought to give a statement of the 
 more important discoveries, upon which the Science of Mine- 
 ralogy is based, in such a form as to be intelligible to those 
 who have hitherto given no attention to the wonders of the 
 Mineral Kingdom, and at the same time to be of service to the 
 student by indicating relations between mineral characters 
 which might otherwise escape attention. 
 
 In addition to the specimens and models selected to make 
 clear the statements and the reasoning of the Introduction, 
 others have been arranged in the window-cases of the Gallery 
 to illustrate in detail the various characters of minerals. 
 
 It may be added that in the description of the minerals 
 of the General Collection the matter interesting or intelligible 
 only to the student has been printed in smaller type, and thus 
 need not perplex the general public* 
 
 Jvme l%th, 1884. L. Plktoheb. 
 
TABLE OF CONTENTS. 
 
 PAGE 
 
 Plan of the Gallery 8 
 
 Genekal Arrangement ; — 
 
 The auxiliary collections ....... 9 
 
 The simple minerals ........ 9 
 
 The rocks 9 
 
 The meteorites ......... 9 
 
 The History of the Collections 10 
 
 The Scope of a Complete Mineral Collection .... 13 
 
 An Introduction to the Study of Minekals .... 17 
 
 The Characters of Minerals 61 
 
 The Recent Additions ........ 70 
 
 The Collections of Crystals and Crystal Models ... 70 
 
 The Pseudomorphs . 71 
 
 The Mineral Species and their Varieties .... 73 
 
 The Pavilion 114 
 
 Index to the MineraiiS mentioned in the Guide . . . 116 
 
Plan oir the Mineral Gallery 
 
 <s- 
 
 1-1 
 
 I" 
 
 
 1^- 
 
 d 
 
 
 1' 
 
 -3S\ j-^-ag-j SulphllltS ^^ -\—X3B- 
 
 \3i-^ilu(Ckt kz-^-l — \sz\ 
 
 ■s3-\--Y-'[! !9-\Si2ica&s [3a\ i PatT] 
 
 -gr-<; 
 
 Slliaaes Fm-^- ; \is\ 
 
 ■-'-■-•j ;-g"s]»S'&Bfeg |-2e-r--! i-vzc-j 
 
 Fzij^Jt&aag [-g^ffl-.- ■ -;-g7| 
 
 
 3 
 
 [^ Ori'i&t [-/g|-|- !---;-/g] 
 
 ^ fizt&f f/^-j r--rM-l 
 
 |-//-| Oxides 
 ^.Oxides 
 
 r ^ 1 1 1 vXldes -I : ; ■ 1 
 
 \!>-r-'\ •:3]ff uorMat k><>-'^ i !-«'l 
 
 !...i..,r.P*"^ 
 
 'jSalta£i 
 
 
 I^Tu^uZvi 
 
 ^' 1 t!i; rsrla feCTWifo l-sTf-rc-t-^i 
 
 Mntrmice- 
 
 ■ti Hit) 
 Gallen/ 
 
 ;>4 
 
( 9 ) 
 
 THE GENERAL ARRANGEMENT OF THE 
 COLLECTIONS. 
 
 By ascending the large staircase opposite to the Grand 
 Entrance and turning to the right, the visitor will reach a 
 corridor leading to the Department of Minerals. 
 
 In a wall-case of the corridor, to the left of the entrance to 
 the Gallery, are shown polished specimens of some of the rocks 
 and simple minerals used for decorative purposes. 
 
 Leaving the corridor the visitor will find the collections 
 arranged in two rooms ; the first of them, the Gallery, 
 measuring 236 feet by 50 feet, the other, the PavUion, 37 feet 
 by 60 feet. 
 
 The AUXILIAET COLLECTIONS are arranged in twenty table- 
 cases placed before the windows of the Gallery. Beginning 
 with the first on the left, the contents of these cases are as 
 follows : — 
 
 I. A series of specimens and models illustrating the gradual 
 
 development of the Science of Mineralogy (page 17). 
 II.-IV. Specimens illustrating the characters of minerals, 
 
 and the terms used in their description (page 61). 
 V. Eecent additions (page 70). 
 VI.-IX. Crystals, natural and artificial (page 70). 
 X.-XIII. Models of Crystals (page 70). 
 XIV.-XX. Pseudomorphs (page 71). 
 The SPECIES AND VABIETIES OF MINERALS are arranged in the 
 remaining table- cases of the Gallery, forty-two in number 
 (page 73). 
 
 The BOCKS are shown in the wall-cases of the Gallery and 
 Pavilion, but are not yet finally arranged. 
 
 The MeteobItes are exhibited in the four central cases of the 
 Pavilion (see the special Guide); 
 
( 10 ) 
 
 THE HISTORY OF THE COLLECTIONS. 
 
 The Minerals formed a very small part of Sir Hans Sloane's 
 collections, of which the acquisition by the nation in 1753 led 
 to the establishment of the British Museum. Consisting, as 
 the mineral portion did, chiefly of wrought articles of agate, 
 jasper and rock-crystal, it failed to represent the variety, the 
 natural forms, or the modes of occurrence of the products be- 
 longing to the Mineral Kingdom. Of these wrought articles, 
 such as are interesting rather for the workmanship bestowed 
 upon them than for the material of which they are made, are 
 deposited at the British Museum (Bloomsbury) ; most of the 
 remainder are shown in the table-cases of the Gallery. 
 
 Through the bequest in 1799 of the collection of very select 
 minerals formed by the Eev. Clayton Mordaunt Cracherode, and 
 the purchase in 1810 of the large collection made by Colonel 
 Greville, including unique specimens of Eubellite, Cromfordite 
 and Matlockite, the Minerals began to form an important part 
 of the Natural History Collections of the ^British Museum. 
 
 In 1823 they were considerably increased by the presentation 
 of a series of specimens from the Harz district by His Majesty 
 King George IV., the silver-yielding minerals being par- 
 ticularly fine. 
 
 During the succeeding years many specimens which had 
 belonged to the private collections of Mr. Heuland and Lady 
 Aylesford were purchased for the Trustees, and at the death of 
 Lady Aylesford the remainder of her minerals, and a catalogue 
 of the complete collection, came to the Trustees by bequest. 
 
 By 1857 the Minerals had become so important a feature 
 of the Museum that a special department, distinct from that 
 of Geology, was instituted, and placed under the Keeper- 
 ship of Mr. Story-Maskelyne, Professor of Mineralogy in the 
 
History of the Collections. li 
 
 University of Oxford. During his term of ofSce, which lasted 
 nearly a quarter of a century, the Trustees were enabled by 
 timely purchases to raise the collection to its present position, 
 and to impart to it a perhaps unrivalled excellence as well in 
 its general completeness as in the perfection of individual 
 specimens. 
 
 The most important additions during this period were the 
 Allan-Greg and the Kokscharow Collections. The first of these 
 had been originally formed by Mr. Eobert Allan of Edinburgh, 
 and catalogued by the distinguished mineralogist Haidinger 
 himself; additions were made to it by the subsequent owner, 
 Mr, Kobert Greg, from whom it was purchased by the Trustees 
 in 1859. It supplied many species previously wanting, and was 
 especially valuable for the authenticity of the localities as- 
 signed to the specimens, in which respect the Museum Collec- 
 tion had at that time fallen much in arrear. Its acquisition 
 gave a new starting point for the Collection of Meteorites by 
 the addition of a carefully formed series of those bodies ; this 
 has since become as complete a collection as can be made. 
 
 The other collection was purchased in 1865 from the 
 eminent Eussian crystallographer. General von Kokscharow; 
 it included a very fine series of Russian and Siberian minerals, 
 among which were specimens of Topaz and Euclase of the 
 greatest rarity. 
 
 The collection formed by Dr. Benjamin Bright of Bristol, 
 presented to the Trustees in 1873, furnished many additional 
 good specimens. 
 
 Of other remarkable specimens presented to the Trustees 
 for the National Collection we may specially mention : — 
 
 The large mass of Meteoric Iron from Otumpa, presented 
 
 in 1826 by Sir Woodbine Parish, F.R.S. 
 
 The jade tortoise, brought from India by Lieut.-General 
 
 Kyd, and presented in 1830 by Thomas Wilkinson, 
 
 Esq, (page 100). 
 
 Several unusually fine specimens, presented in 1836 by 
 
 Richard Simmons, Esq., F.B.S,, including specimens 
 
 of Native Gold (Case Id), Cerjissite (Case 18c), Idocrase 
 
 (Case 25e), Beryl (Case 30a) and Mimetesite (Case 40g), 
 
 A series of minerals from Greenland, including fine 
 
12 History of the Collections. 
 
 specimens of Columbite (Case 34g),presented in 1855 by- 
 Joseph Walter Tayler, Esq., P.G.S. 
 
 The Pamallee and Nellore Meteorites, presented in 1858 
 and 1862 respectively by Sir William Denison, K.C.B., 
 Governor of Madras. 
 
 A fine specimen of Cerussite (Case iSc), presented in 1859 
 by John Taylor, Esq., P.R.S. 
 
 A fine series of Apophyllites and Stilbites from India, 
 presented in 1860 by James J. Berkley, Esq. ; most of 
 the specimens are arranged in a wall-case of the Pavilion. 
 
 Meteorites from Durala, Dhurmsala, Shalka, Bnstee, 
 Monza Khooma and Udipi, presented (1861-9) by the 
 Secretary of State for India in Council. 
 
 Meteorites from many Indian localities, presented (1861-2) 
 by the Asiatic Society of Bengal. 
 
 The Cranbourne Meteorite, presented in 1862 by James 
 Bruce, Esq. 
 
 A beautiful specimen of RnbeUite from Ava (Case 33a), 
 presented in 1869 by C. S. J. L. Guthrie, Esq. 
 
 A magnificent specimen of Proustite, the light-red silver 
 ore (Case 8b), presented in 1876 by Henry Ludlam, 
 Esq., F.G.S. 
 
 A meteorite from Japan, presented in 1883 by Naotaro 
 Nabeshima, Esq. 
 
 During the last forty years specimens have been frequently 
 presented by William Garrow Lettsom, Esq., and 
 Professor John Buskin : among those given by Mr, 
 Lettsom may be noted the nearly unique specimen of 
 Whewellite (Case 39h), the Epidotes from Traversella 
 (Case 27d), and the Apatite from New York (Case 
 40b) ; and, among those given by Prof. Eusbin, the pink 
 crystals of Fluor from Switzerland (Case 7g), the long 
 branch of Native Copper placed in the lower part of 
 Case 1, and many specimens of Native Silica shown 
 in a table-case of the Pavilion. 
 
THE SCOPE OF A COMPLETE MINERAL 
 COLLECTION. 
 
 A Mineral collection, in order to be complete, must aim at 
 presenting all the definite varieties of chemical composition of 
 the distinct mineral substances which occur in the Earth's crust, 
 and at the same time must illustrate the often very extensive 
 varieties of crystalline form assumed by the minerals of a species 
 or group. But besides these chemical and morphological fea- 
 tures other important characters have to be illustrated, among 
 which are the various modes of occurrence of each particular 
 mineral, including its associations with other minerals ; and in 
 a great national collection that is to illustrate the mineralogy 
 of the world, it is important that there be specimens from 
 all localities where a mineral occurs under special and note- 
 worthy circumstances ; and it must be a special object that 
 examples of each mineral species should show its most com- 
 plete development, whether in magnitude or perfection of 
 crystals, in the colour and limpid purity, or in any other im- 
 portant quality which may belong to it in its more excep- 
 tional occurrence. 
 
 In a mineral collection formed and arranged with these 
 purposes in view, will be found materials of the greatest 
 interest for science, and alike for the useful and ornamental 
 arts : to the crystallographer, it offers some of the best illus- 
 trations of a most beautiful geometrical science ; to the phy- 
 sicist, it provides the material on which some of the most 
 refined and important investigations have been and may be 
 made in connection with the theories of light, heat, magnetism 
 and electricity; and to the geologist, its petrological depart- 
 ment presents the means for discriminating those minerals, 
 of which, though they are often only recognisable under 
 the microscope, the largest portion of the Earth's crust is 
 formed. 
 
14 The scope of 
 
 Here will be found, in all their variety, beauty and associa- 
 tion, the minerals which, under the name of ores, furnish the 
 metals so essential to the needs and happiness of man ; here 
 also are specimens of the numerous minerals which, whether 
 immediately or as the sources from which manufacturers derive 
 important products, are employed in the multifarious purposes 
 of daily life. The suggestion that materials for construction 
 and architectural ornament, for pigments, mordants and bleach- 
 ing processes, that the phosphates for manures, the alkalies, and 
 the materials for the manufacture of acids, are all largely 
 dependent on the mineral resources of the world, will suffi- 
 ciently show how intimately a complete mineral collection is 
 connected with the arts and with commerce. 
 
 An illustration of the importance of a single mineral is 
 afforded by Calcite or carbonate of lime. As the almost ubiqui- 
 tous limestone, it supplies in some of its varieties the building 
 materials of our cities ; and when burnt gives quicklime, and in 
 some of its impurer forms hydraulic cement ; while in other 
 varieties it presents itself as the white and spotless material 
 used for statuary marble ; or, again, beautifully and finely 
 coloured, forms the infinitely varied ornamental marbles ; 
 sometimes it appears as calcspar in a thousand crystalline 
 forms, which it takes the skill of a crystallographer to reduce to 
 a common symmetry ; or, again, as' in one locality in Iceland, it 
 occurs in large masses of limpid crystal conspicuous for its 
 double refraction, a character which rendered it invaluable in 
 the hands of Bartholinus, Huyghens and Fresnel, for the 
 investigation of the properties of light ; or, again, in its softer 
 form of chalk, it subserves many a domestic use. 
 
 Here also are to be found . rough and cut specimens of the 
 precious stones, among which may be mentioned the Diamond, 
 a crystallised form of the element carbon ; the Balas ruby and 
 the Spinel ruby, a compound of alumina and magnesia; the 
 Chrysoberyl and Alexandrite, a combination of alumina and 
 beryllia ; the Sapphire and Kuby, the sesquioxide of aluminium ; 
 the Hyacinth and Jargoon, a compound of silica and zirconia ; 
 the Amethyst, Sard, Plasma, Prase, Chalcedony and Noble 
 Opal, varieties of silica; the Chrysolite and Peridot, a 
 silicate of magnesium and iron ; the Garnet with a varied 
 
a complete mineral collection. 15 
 
 composition ; the Bery], Emerald and Euclase, compound 
 silicates of aluminium and beryllium; the Tourmaline and 
 Eubellite, a borosilicate of several bases ; the Lapis-Lazuli, a 
 compound silicate and sulphate ; and the Turquoise, a hydrated 
 phosphate of aluminium. 
 
 Petrology, so far as it is a classificatory science, it is 
 essentially the function of a mineralogist to study and illustrate. 
 The interest presented by a rock is not merely dependent upon 
 its chemical composition, though that is a fundamental principle 
 in describing it, nor upon its being a compact aggregation of 
 the various minerals among which the chemical ingredients 
 are distributed ; but it is also historical, since the rock has 
 assumed the form, in which we observe it, at some earlier 
 period of geological time. To trace that history, and to 
 collocate the various rocks of the globe in their relative positions 
 and historical sequence, and to make each rock contribute its 
 evidence towards the building up of that history, is the part of 
 the geologist. But it falls entirely to the mineralogist to 
 collect, describe and classify the almost numberless varieties 
 of rock with which the geologist has to deal. 
 
 And to describe a rock with accuracy is perhaps the most 
 diificult task that the mineralogist has to perform. It is 
 possible to make a complete chemical analysis of the whole 
 of a rock-fragment, but the cases in which the individual 
 minerals that compose the fragment can be isolated and 
 separately analysed are extremely rare. The microscope, 
 however, has been called in to raise the power of human 
 introspection ; under that instrument not only are the mineral 
 ingredients of a thin slice of a rock — so thin as to be per- 
 fectly transparent — rendered visible, but the action of each 
 separate ingredient upon the transmitted light can be easily 
 ascertained. By combining the instruction gained from tho 
 chemical analysis of rock-fragments with the results of such a 
 microscopic study, the mineralogist, after a long and intimate 
 experience, is enabled to speak, with at least an approximate 
 certainty, of the characters and even the chemical composition 
 of the various constituent minerals of each kind of rock. 
 
 The great divisions of a petrological series are readily 
 marked out, though their precise boundaries are not always 
 
16 Scope of a complete mineral collection, 
 
 so easy to define. We have, for instance, the sedimentary 
 rocks, sometimes composed largely of a single ingredient, as 
 the sandstones and limestones, at other times less simple in 
 their nature, as the clays, shales and slates. Again, we have 
 the igneous rocks, comprising, on the one hand, lavas and beds 
 of ash and pumice that have been poured out or ejected from 
 orifices in the Earth's crust, and, on the other hand, the 
 more compact forms which have cooled from a condition of 
 fusion, or semi-fusion, under the pressure of superincumbent 
 strata. Again, there are rocks of an intermediate character, 
 in which a sedimentary deposit has become metamorphosed 
 in the course of time under the combined influences of pressure 
 and temperature. 
 
 Nor from the list of the interesting contributions of a 
 mineral collection should be omitted the series of meteoric 
 bodies which have come to this Earth from the regions of space. 
 These strange masses of metallic iron, more or less rich in 
 nickel, or of stone impregnated with the same metallic material, 
 serve as witnesses that the same laws of chemical combination 
 and of crystaUographic symmetry, and the same elements, of 
 which our own world is built up, pervade the regions of space 
 through which these masses of matter have wandered swiftly 
 till, entangled in our atmosphere, they have been arrested 
 in their career and have fallen to the Earth with startling 
 accompaniments of explosion, fusion, and dissipation of their 
 material, as a consequence of the enormous temperature for 
 which they have exchanged an often more than planetary 
 velocity. 
 
AN INTRODUCTION 
 
 STUDY OF MINERALS. 
 
 The specimens and models illustrative of this Introduction are arranged in the 
 first window-case on the left-hand side of the Gallery. 
 
 Ti>e 1. The material products of Nature are assigned to three Specimen 
 Kingdom. Kingdoms, — ^the Animal, the Vegetal and the Mineral; the " ""'' 
 distinguishing character of the products belonging to the two 
 former being the presence of organs essential to the existence 
 and growth of the individual. 
 
 The distinction, however, is not always very obvious, for Specimens 
 in some cases the outer form of a mineral product is "^ ., 
 
 ^ pyroiusite 
 
 so like that of a plant that it misleads the ordinary and 
 
 observer. moss-agate. 
 
 Its extent, 2. The Mineral Kingdom includes not only the unorganised Specimen. 
 products of our own Earth, but also those which belong to outer 
 space : some knowledge of the latter has been gained directly 
 by examination of the bodies called Meteorites which have 
 fallen from the sky ; and also, indirectly, by a study of the 
 light which reaches us from the sun, the stars and the comets. 
 These investigations have not yet indicated the existence of 
 life outside our own planet. 
 The 3. It is practically possible to obtain a direct knowledge of 
 
 Science ^^^ mineral products of our own Earth within only a mile or so 
 Mineralogy, from its surface; but the considerationof even this limited amount 
 of matter is far too vast for one individual or one science. 
 
 The present an-angement into hill and dale, river and sea 
 is accordingly left to Geography, and the historical aspect of the 
 
18 Rocks and Minerals. 
 
 materials to Geology; the Mineralogist deals, not with the 
 arrangement past or present, but with the nature of the matter 
 itself ; he determines as far as possible all its characters, and 
 thence deduces principles on which to classify the various 
 kinds. 
 Soil. 4. The first mineral product met with in the examination Specimen. 
 
 of the solid portion of the Earth is usually a loose Soil, 
 which on inspection is found to be a mixture of fragments of 
 substances of different kinds, and to have resulted from the 
 wearing away of the more compact matter in the neigh- 
 bourhood. 
 Kock. 5. Beneath the loose soil is a firmer material, retaining Specimen 
 much the same character generally over a considerable area of "^^l^' 
 country and sometimes for a considerable depth ; to such a 
 material the terra Kock is applied. 
 
 Rocks are As in soil, SO also in most kinds of rock the unaided eye Specimen. 
 
 generally jg ^^ t^ detect different kinds of matter. 
 
 composite. . . , . „ 
 
 The illustrative specimen m the case is a fragment of the 
 rock called Granite; mere inspection teaches us that 
 in this specimen at least three different kinds of matter 
 come together — first, a substance of a light brown colour, 
 with some of its surfaces quite smooth and plane 
 (Felspar) ; secondly, a glassy substance of a milky 
 colour and irregular shape (Quartz) ; and, thirdly, a 
 dark-coloured substance apparently made up of thin 
 leaves (Mica), By a process of mechanical division 
 we can thus extract from this kind of rock at least 
 three substances; and these will prove to be distinct 
 from each other, not only in outward appearance, but in 
 all their manifold properties. 
 Simple 6. It will be found, however, that by no amount of mechanical Specimens 
 minerals, ^jyigjon can any of these three substances be reduced to 
 others having different characters; they are therefore called 
 Simple Minerals, or, more briefly, Minerals, 
 other 7. The composite character of some rocks is less evident to Specimen 
 rocks. ^^ naked eye, and requires the aid of a microscope for "'' 'l'»''*^« 
 its dbmonstration. 
 
 Other rocks, as Marble, are of a simpler nature than the Specimen, 
 above^ and consist wholly of a single kind of matter. 
 
Modes of occurrence. 19 
 
 Rock- 8. Up to the present we have had regard only to those 
 
 mi^rafs ™iiierals which are scattered more or less regularly throughout 
 
 are not the whole mass of a rock, and are therefore considered to be 
 
 dififemit ^sseniiaZ components of it. Although such simple minerals 
 
 liiods. compose the greater portion of the crust of the Earth, their 
 
 kinds are extremely limited in number. 
 
 Modes of ^' ■^'^t in addition to their essential components, rocks 
 
 occurrence contain, either completely embedded or lining crevices and 
 
 simple cavities, many other simple minerals, more or less irregular 
 
 minerals, or local in their occurrence. 
 
 Gold, for instance, has not*been found either as a rock or Specimens, 
 as an essential component of one, but it often occurs as 
 an accessory constituent completely embedded in a part 
 of a rock. From a side of the cavity of the next 
 specimen in the case springs a beautiful mineral 
 (Scolecite), showing no likeness to any essential com- 
 ponent of the enclosing rock (Dolerite) ; and a like 
 remark may be made with respect to the simple sub- 
 stance (Wavellite) which lines the sides of the two parts 
 of the adjacent one (Sandstone). In fact, it is from rock- 
 cavities, filled with foreign matter and constituting veins 
 and lodes, sometimes of enormous size, that most of the 
 mineral wealth of the world is derived. 
 Sometimes simple minerals are found as loose waterworn Specimens 
 pebbles on a sea-shore or in the bed of a stream. ^'^, 
 
 ^ coiundum. 
 
 Fluid 10. In addition to the solid unorganised products of Nature, 
 minerals, t^jere are others which are liquid or gaseous at the ordinary 
 temperature ; as they are few in number and generally mix- 
 tures, with the exception of the liquid Mercury they will be 
 left out of consideration in the following pages. 
 
 11. The existence of simple minerals is so elementary a fact 
 that it must have been more or less distinctly recognised from 
 the earliest times. But to determine the properties of each kind 
 of simple mineral so far as to be able to assert that one speci- 
 men is of the same kind or is different from another, and to 
 classify the various kinds, are difficulties of a very serious 
 character. A brief sketch oi the gradual development of the 
 
 B 2 
 
20 Distinction into kinds. 
 
 Science of Mineralogy will perhaps be the most instructive 
 mode of explaining the nature of these difSculties and the 
 ways in which they have been met* 
 
 Distinction 12. The modem student relies so much on crystalline form 
 "into^Hnds^ and chemical composition as distinguishing characters, that he 
 by the is at times almost inclined to believe that without a knowledge 
 ancients, pf ^jjese any distinction into kinds must have been impracticable ; 
 and yet, to give only a single instance, the diamond was re- 
 cognised as a distinct mineral, and distinguished by a special 
 name, quite two thousand years before its combustibility and 
 its chemical identity with carbon had been discovered. 
 
 In the oldest existing treatise on Minerals f vi'e are told how 
 the subject was treated more than two thousand years ago. 
 
 Minerals were then classified as Metals, Stones and Earths. 
 The class of Metals included, not only the metals proper, but 
 all those minerals which are dense and have a metallic lustre ; 
 that of Stones contained those which are unacted upon by 
 water, while the Earths were minerals which, when placed 
 in water, either fall to pieces or are dissolved therein. 
 
 The following extract from the treatise referred to will show 
 what were the properties then used for the distinction of 
 "■Stones" into kinds: — 
 
 "There are in Stones of different kinds many peculiar 
 qualities ; of which colour, transparency, brightness, 
 density, hardness, tena,city and the like are frequent, 
 though other more remarkable properties are not so 
 common. But beside these qualities there are others ; 
 such as their acting upon other bodies, or being 
 subject or not subject to be acted upon by them. Some 
 are fusible, others will never liquefy in the fire ; some 
 may be calcined, others are incombustible ; to which it 
 may be added that in the action of fire on them they 
 show also many other differences. Some, as Amber, 
 have an attractive quality. Others serve for the trial 
 of Metals, as the Lydian stone. 
 
 * See also Whewell's History of the Inductive Sciences. London, 1857. 
 t History of Stones ; written by Theophrastua shortly before 300 b.o. : 
 English version by John Hill. London, 1746. 
 
Experiment necessary. 21 
 
 " But the most known and general properties of Stones are 
 their several fitnesses for the various kinds of work. 
 Some of them are proper for engraving on ; others may 
 be shaped by the turner's tools ; others may be cut or 
 sawn. Some also there are which no iron instruments 
 will touch, and others which are very difficultly, or 
 scarcely at all, to be cut by them." 
 Experiment i3_ Amone the characters mentioned above there is not a 
 
 necessary. ... tti i n-n 
 
 Single important one, appealing directly to the sense of sight 
 alone, which will serve for the distinction of minerals into kinds ; 
 for colour, transparency and brightness are either too common 
 or too inconstant to be of much avail. The fact that the most 
 important distinguishing characters require experiment for 
 their determination, and thus cannot be learned from a mere 
 inspection of the specimens as they lie in a table-case, is the 
 chief reason why a collection of Minerals is so much more 
 difficult to understand than is one of organised bodies. 
 
 Origin of 14. In the course of time another important and general 
 'c* sta" ^^* -^^^^ obvious character came gradually into recognition. 
 
 To a certain mineral the ancients gave the name Crystal Specimens. 
 (i.e. clear ice), for, owing to its transparency, its freedom 
 from colour, and the frequency with which it enclosed other 
 bodies, the ancients imagined that it had been formed 
 through the subjection of water to an intense cold. Even 
 so lately as the year 1672 this theory of the origin of 
 Crystal is referred to by the learned experimenter, Eobert 
 Boyle, * in the following words : — 
 
 " I found the weight of Crystal to be to that of water of 
 equal bulk as two and almost two-thirds to one ; which, 
 by the way, shows us how groundlessly many learned men, 
 as well ancient as modern, make Crystal to be but ice 
 extraordinarily hardened by a long and vehement cold, 
 whereas ice is, bulk for bulk, lighter than water (and 
 therefore swims upon it), and (to add that objection 
 
 * An Essay about the Origine and Virtues of Gems ; by Robert Boyle. 
 London, 1672. 
 
22 Constancy of the 
 
 against the vulgar error) Madagascar and other countries 
 in the Torrid zone abound with Crystal." 
 "Crystal" It was observed by the ancients that this mineral, wherever 
 'typi°4^^ found, has a characteristic shape (Fig. 1). It is naturally 
 
 surfaces. 
 
 Fig. I. 
 
 bounded by fiiat surfaces (or planes) arranged in a definite way 
 
 — six of them forming a column (or prism), at each end of 
 
 which are arranged six other planes inclined to form a pyramid. 
 
 The relative sizes and the shapes of these planes vary in 
 
 different specimens. 
 
 Later 15. This peculiarity of being naturally bounded by flat sur- Specimeni. 
 
 "^hTtenn f^ces, and not by the curved ones which are so characteristic 
 
 Crystal, both of Plants and Animals, was afterwards found to belong not 
 
 only to " Crystal " but to other minerals both transparent and 
 
 opaque; so that by an extension of its meaning the term 
 
 Crystal was eventually used to signify, not the particular kind 
 
 of mineral still known as Eock-crystal, but any mineral 
 
 naturally limited by plane faces. 
 
 steno's 16. It was not till 1669 that any important addition to the 
 
 discorery. jjnowledge of the properties of minerals was made. In that 
 
 year Nieolaus Steno,* a Danish physician, announced that, 
 
 amid all the variations in the sizes and shapes of the faces of 
 
 the mineral termed Kock-crystal, there was something constant 
 
 besides the number and the grouping of the faces. Cutting 
 
 each of a series of specimens in a direction at right angles to 
 
 the edges of the prism, he found that the edges of the six- 
 
 * De solido intra solidum naturaliter contento dissertationis prodromus. 
 FlorentiEB, 1669 : BDglish translation, London, 1671. Kgs. 2 and 3 are repro- 
 ductions of figures given by Steno. 
 
angles of rock-crystal. 23 
 
 sided sections thus obtained vary in length, and thus form 
 figures apparently quite distinct from each other (Fig, 2). 
 
 No- 
 
 Fig. 2. 
 
 On careful examination of these figures, Steno found that 
 although the sides vary in length they do not vary in 
 inclination to each other; that iu fact the angles of any one 
 figure are equal both to each other and to every angle of each 
 of the remaining figures. Again, making sections of the speci- 
 mens in another direction, namely, at right angles to the edge 
 formed by a face of a pyramid with a face of the prism, he 
 obtained such figures as the following (Fig. 3) : — 
 
 V 
 
 Fig. 3. 
 
 The angles of any one of these figures are not, as in the 
 previous case, all equal to each other ; two of them, the opposite 
 and equal angles h, are different in size from the remaining 
 four equal angles e, while both h and c are distinct in size from 
 the angles a of the previous figures. And in the case of each 
 of the specimens examined, Steno found that when the section 
 was made in the stated direction he always obtained a figure 
 having two angles equal to h and four angles equal to c, 
 except when the absence of the prism led to a four-sided figure 
 with two opposite angles equal to &, as shown in Fig. 3. 
 
 Hence he inferred that in all specimens of Rock-crystal 
 corresponding pairs of faces have the same inclination. 
 
 17, A simpler method of procedure is to cut an angle in 
 cardboard into which an angle of one of the specimens will 
 just fit, and then to show that this is likewise the case with a 
 corresponding angle of any other specimen. 
 
24 Crystallisation. 
 
 steno's ex- 18. To account for this property Steno made the following 
 
 planation. . . 
 
 suggestions : — 
 
 1. Eock-crystal has once been liquid ; as is shown by the Specimens, 
 way in which it encloses other bodies. 
 
 2. Eock-crystal may increase in size ; as is proved by the Specimens, 
 fact that sometimes stages in the growth are indicated 
 
 by the positions of the enclosures. 
 
 3. The original nucleus, owing to the "nature of Eock- 
 crystal," assumed the form of a regular six-sided prism, 
 terminated at each end by a six-sided pyramid. 
 
 4. The increase is due to the deposit of layers of matter 
 upon tlie faces of the nucleus. 
 
 5. The thickness of the layer deposited upon a given face 
 is the same in all its parts ; the outer surface will 
 therefore still be plane and be parallel to the face upon 
 which the layer is deposited ; hence the angles between 
 the faces will remain constant in size during the growth, 
 
 6. The thickness of a layer, though constant for various 
 parts of the same face, is different for different faces, 
 owmg to the variety of their positions relative to the 
 surrounding liquid ; the faces themselves may thus vaiy 
 considerably both in size and shape. 
 
 These suggestions," though on the whole satisfactory,, fail to Specimen, 
 account for the presence of faces additional to the more 
 prominent ones already referred to ; and yet such additional 
 faces are of common occurrence. 
 
 Crystalli- 19. The specimens of no other mineral being so similar to 
 sation. Q^^ other in form as those of Eock-ciystal, a whole century 
 passed away before any extension was given to the law 
 announced by Steno. In the meantime it was found that a 
 natural limitation by plane faces is to be met with, not only 
 in the Mineral Kingdom, but whenever any dissolved substance 
 reappears, in the solid state through the evaporation of the 
 solvent; and that when the evaporation is slow and the dis- 
 turbance small, very perfect crystals are the result. Crystals, Specimens, 
 thus obtained have been termed artificial. It was further 
 remarked that to some extent the shape of a crystal depends 
 
A primitive form. 25 
 
 on the kind of substance dissolved ; common salt reappears 
 as cubes, alum as octahedra, blue vitriol in rhomboidal forms, 
 and nitre as prisms. It thus came to be imagined to be a 
 general law of Nature that when the particles of a body are 
 separated by a fluid and thus made free to move, they tend to 
 arrange themselves into regular shapes, limited by plane faces, 
 when the fluid disappears. Still, although it was recognised 
 that the shape of a crystal depends in some way or other on 
 the nature of the substance, it was found that the dependence 
 was not a simple one, for, even with the same substance, very 
 diflerent shapes of crystal may be obtained. 
 
 Rom^ de 20. To Rom6 de I'lsle * belongs the great credit of discover- 
 ' '' * ing that these various shapes of crystals of the same natural 
 or artificial product are all intimately related to each other. 
 
 According to his theory the shape of every crystal of the 
 same substance is such as can be derived by a particular 
 
 Primitive process from a certain fundamental figure called the Peimitive 
 °™' FORM, the shape and angles of which depend only on the 
 nature of the substance itself. The process consists simply in 
 the replacement of the edges or the solid angles (corners) of 
 the primitive form by single planes or by groups of planes, but 
 always in such a way that the total alteration is similarly 
 related to all parts of the -primitive form which are geome- 
 trically similar; these planes of replacement he regarded as 
 secondary and more or less accidental. With a view to the 
 development of this theory, Rome de I'lsle proceeded to deter- 
 mine the shape of the primitive form of every kind of known 
 substance, whether natural or artificial ; and he was able to do 
 this with a certain degree of precision by means of an instru- Specimen. 
 
 luTention mcnt for the measurement of angles, invented by Carangeot, 
 ?^^ , to whom he had entrusted the preparation of some of the clay- 
 models intended to illustrate his theory. He was thus led to 
 the discovery that the angles between the faces of a primitive 
 form are always the same for the same kind of substance, and 
 are characteristic of it. For example, he found that while 
 the primitive form of alum, nitre and sugar is in each case an 
 
 * Bssai de Cristallograpbie. Paris, 1772. Cristallograpliie, ou description 
 des formes propres 4 tous ies corps du rfegne mineral. Paris, 1783. 
 
26 
 
 The kinds of primitive Jorm. 
 
 octahedron, the angles of the primitive forms are different, for 
 that which iu alum is always 110°, is 120° in nitre and 100° in 
 sugar. 
 
 Kinds of 21. The different kinds of primitive form met with by Models, 
 primitive jJq^^ (jg I'lsle in his examination of natural and artificial 
 
 form, 
 
 crystals were only six in number (Fig. 4), namely : — 
 
 Fig. 4. 
 •' a. The cube, 
 
 h. The regular octahedron, 
 e. The regular tetrahedron, 
 
 d. The rhombohedron, 
 
 e. The octahedron with a rhombic base, 
 /. The double six-sided pyramid. 
 
 In the first three of these figures there can be no variety 
 since they are by definition fixed in their angles, but in the 
 lartter three there may be any number of shapes due to difference 
 in angle. 
 
 22. To make the theory of Eome de I'lsle more clear it will 
 be necessary to enter a little into detail ; and in the first place 
 we shall trace the varieties of crystalline form which his theory 
 would lead one to expect to meet with in a mineral having the 
 cvhe for primitive form. The illustrative specimens belong to 
 the mineral Fluor. 
 Modifica- The faces of a cube being six equal squares, they are Model and 
 *'Tube!''* geometrically similar : all the twelve edges are likewise Specimen, 
 geometrically similar, for they are of equal length and are 
 formed by faces meeting at the same inclination, iiamely, a 
 
Theory of Romi de risk. 
 
 27 
 
 right angle : all the eight solid angles are geometrically similar, 
 for each of them is formed by the meeting of three similar 
 edges all intersecting at the same inclination, a right angle. 
 Any natural alteration of an edge of this primitive form we 
 may expect to be similarly related to the two similar faces 
 meeting in the edge, and any natural alteration of a solid 
 angle to be similarly related to the three similar edges 
 meeting in the solid angle ; further, we may expect the same 
 alterations to be repeated on all the similar edges and solid 
 angles of the figure. 
 
 1. If an edge of the cube be replaced by a single face, the Model and 
 face must be equally inclined to the two similar faces p''^""'"- 
 meeting in the edge ; and this alteration must be repeated on 
 all the edges, since they are similar (Fig. 5). 
 
 ^ 
 
 i^ 
 
 Fig. 5. 
 
 Fig. 6. 
 
 2. If an edge be replaced by a face unequally inclined to Model and 
 the two faces meeting in that edge, a second face must also be ^P*''™®"' 
 present to make the total alteration similar with respect to 
 
 the similar faces ; and a similar pair of faces must replace 
 each of the remaining edges (Fig. 6). 
 
 3. If a solid angle be replaced by a single face, the face Models and 
 must cut off equal lengths from the three similar edges Specimens. 
 forming that solid angle; and a similar face must replace 
 
 each of the other solid angles. 
 
 As these new faces increase and the faces of the original cube 
 
 Kg. 7. 
 
 Fig. 8. 
 
 Fig. 9. 
 
 Fig. 10. 
 
 diminish in size, there is a gradual transition from the cube to 
 the regular octahedron (as shown in Figs. 7, 8, 9, 10). 
 
28 
 
 Its application to the cube. 
 
 4. Of the latter figure the faces, edges and solid angles are 
 respectively similar. Hence, just as in the cube, if an edge be 
 replaced by a single face, the face must be equally inclined 
 to the two similar faces meeting in the edge ; and the 
 alteration must be repeated on all the remaining edges (Fig. 11). 
 
 Model, 
 
 Fig. 11. 
 
 Fig. 12. 
 
 ' 5. And again, a solid angle of the last figure may be replaced Model and 
 by a single face cutting off equal lengths from the edges Specimen, 
 meeting in the solid angle ; and the alteration must be 
 repeated on'the remaining solid angles (Fig. 12J. 
 
 6. Returning to the cube, if a face replacing a solid angle cut Model, 
 off equal lengths from two of the edges, but a different length 
 from the third edge, meeting in the solid angle, the total 
 alteration will only be similarly related to the three similar 
 edges if two additional faces come into existence ; and a 
 similar group of three faces must replace each of the remaining 
 solid angles (Fig. 13). 
 
 A 
 
 Fig. 13. 
 
 Fig. 14. 
 
 7. And, finally, if a face replacing a solid angle of the cube Model and 
 cut off unequal lengths from the three edges which meet in the Specimen. 
 solid angle, the total alteration will only be similarly related to 
 the three similar edges if five other faces come into existence ; 
 and a similar group of six faces must replace each of the . 
 remaining solid angles (Fig. 14). 
 
 23. To make the theory still more clear we shall now apply 
 it to the more difficult case where the primitive form is a 
 rhomho'hedron : the relation between the derived forms will be 
 more evident to the reader if he refer to the exhibited models, in 
 which corresponding edges or faces are indicated by an identity 
 
The similar parts of a rhombohedron. 29 
 
 of colour, rather than to the figures given in the text. The 
 specimens illustrating the varieties of form are selected from 
 the mineral Calcite. 
 The We must first ascertain which are the similar edges and 
 
 hedron.' similar solid angles of such a figure. 
 
 Like the cube, the rhombohedron (Fig. 15) has six equal Model and 
 faces, each bounded by four equal edges ; it differs from the Specimen. 
 cube in that the angles formed by these four edges instead of 
 being all equal are only equal in pairs, one o'f which we may 
 denote by a and the other by h. 
 
 Fig. 15. 
 
 Its similar 1^ HOW the rhombohedrou be examined, it will be found that 
 solid t^yo opposite solid angles are geometrically similar to each other, 
 "°^ ™' each being contained by three plane angles a ; but that these 
 are different from the remaining six, which are in turn similar 
 to each other, each being contained by two plane angles h and 
 one plane angle a. Each of the first pair of similar solid angles 
 is denoted in the figure by the letter A, and each of the 
 remaining six by the letter B. 
 
 Its similar We have seen above that all the edges are equal in length ; 
 edges, edges are, however, not geometrically similar unless they are 
 formed by similar pairs of planes making the same angle with 
 each other, or when they join similar pairs of solid angles. 
 Thus the six edges denoted in the figure by the letter E are 
 similar in that each of them joins a solid angle A to a solid 
 angle B ; but tliey are not similar to the six zig-zag edges 
 denoted by the letter P, for these join only the solid angles B. 
 
30 Some possible modifications 
 
 Or again, we have seen that each of the solid angles A is 
 formed by three edges E having the same inclination to each 
 other, namely, the angle a ; whence it follows that the edges 
 B are formed by planes having equal inclinations and are 
 geometrically similar to each other. Also, since three edges 
 which meet to form a solid angle B, are unequally inclined 
 to each other, they cannot be all geometrically similar; the 
 two edges P, however, make the same angle l with the edge 
 B, and are so far similar to each other but not similar to B ; it 
 is further seen that the two edges P are contained by planes 
 making the same angle, and that the angle is different from 
 that between tbe planes which meet in the edge B. 
 
 Hence we conclude, that in a rhombohedron there are, from 
 a geometrical point of view, two similar solid angles A, and six 
 similar solid angles B ; six similar edges B, meeting by threes 
 in the pair of solid angles A, and six similar edges P, arranged 
 in zig-zag form and passing by pairs through the six solid 
 angles B ; but the solid angles A are not similar to the solid 
 angles B, nor the edges B to the edges P, 
 
 We now proceed to indicate some modifications of form 
 •which will be consistent with the theory enunciated by Bome 
 de risle. 
 Modifica- 1. Each of the similar solid angles A may be replaced by a Model and 
 ^'Zmbo?^ single face cutting off equal lengths from the three similar Specimen, 
 hedron, cdges B meeting in the solid angle (Fig. 16). 
 
 Fig. 16. 
 
 2. Bach of the similar edges B of Fig. 17 (which represents Model? an^ 
 a new position of the same rhombohedron) may be replaced by Speoimens. 
 a single face equally inclined to the pair of faces meeting therein ; 
 
 as the new faces increase and the old faces diminish in size, 
 there is a gradual transition to a more obtuse rhombohedron 
 (Figs. 17, 18, 19 and 20). 
 
 3. Each of the set of six similar solid angles B of this new rhom- Models and 
 bohedron (Fig. 21) may be replaced by a single face, cutting off Specimens. 
 
of a rhombohedron. 
 
 31 
 
 equal lengths from the two similar edges and a different length 
 from the third dissimilar edge meeting therein ; if one of these 
 
 Fig. 17. 
 
 Fig. :8, 
 
 Fig. 20. 
 
 new faces be parallel to the line joining the pair of similar solid 
 angles A, the remaining five faces will also be parallel to it and 
 the six faces will form a regular six-sided prism; in Fig. 22 
 the faces of the prism are smaU, and in Fig. 23, large. 
 
 <c:^^^ 
 
 re 
 
 
 
 
 
 i 
 
 Fig. 21. 
 
 Fig. 22. 
 
 Fig. 23. 
 
 Fig. 24. 
 
 4, And again, each end of the last figure may be replaced by a Model and 
 single face cutting the six similar edges of the prism at the Specimen, 
 same inclination, a right angle (Fig. 24). 
 
 5. Returning to the original rhombohedron (Fig. 25), each of Model, 
 the six zig-zag edges P may be replaced by a single face equally 
 inclined to the pair of similar faces meeting therein (Fig. 26). 
 
 Fig. 25. 
 
 Fiar. 26. 
 
 Fig. 27. 
 
 Fig. 28. Fig. 29. 
 
 6. If, on the other hand, a face replacing one of these edges Model and 
 P be unequally inclined to the two faces meeting in the edge, Specimen. 
 a second face must come into existence to make the total 
 alteration similarly related to the similar f^ces; and a similar 
 
32 The theory of Rome de I' Isle 
 
 pair of faces must replace eacH of the remaining edges P 
 (Fig. 27). 
 
 7. If the new faces increase until the old ones disappear, the 
 resulting form is that shown in Fig. 28. 
 
 8. And finally, each of the set of six similar solid angles of the Model and 
 last figure may be replaced by a single face parallel to the line %^"»'«"- 
 joining the pair of similar solid angles, thus giving rise to the 
 shape shown in Fig. 29. 
 
 24. Such is the way in which Eome de I'lsle connected 
 together the various crystalline forms met with in the same kind 
 of mineral. Some idea -of the great advance in the knowledge 
 of the forms of crystals which we owe to this mineralogist 
 may be gained from an examination of the clay-models made 
 for him by Lermina and Carangeot to illustrate the Treatise 
 of 1783. One of these sets, which were the first ever made 
 to illustrate a theory of crystals, is shown in window- 
 case X. 
 
 Di6Gcnitiea 25. The theory was extremely successful in indicating that the 
 of the ^ crystalline forms of a mineral belong to one connected series. 
 Its weak point was that the whole series could be derived in 
 this way, not only from the primitive form itself, but from 
 almost any one of the figures of the series, and that thus no 
 hard and fast rule could be given for the determination of the 
 tiTie primitive ; Eome de I'lsle himself was guided in his choice 
 of the primitive by largeness of development and frequency of 
 occurrence of particular faces, and by the simplicity of character 
 of the figure formed by them ; but in practice such a method 
 presents great difficulties. It was owing to this mode of choice 
 that he was led to adopt both the cube and the regular 
 octahedron as distinct primitive forms, although, as we have 
 seen, they are really terms of one series, and can be derived 
 the one from the other by similar alteration of the similar 
 solid angles. 
 
 26. Many of his contemporaries, however, went so far as to 
 doubt not only the accuracy of his choice of the primitive form, 
 but the very existence of the series ; and, ten years aftet 
 the publication of the Essay on Crystallography, we find the 
 
not immediately accepted. 33 
 
 Bnffon. illustrious Buffon,* in his Natural History of Minerals, treating 
 of the new science as follows : — 
 
 " It has been claimed that crystallisation in rhomboheJra 
 is the specific character of Calcite ; neglecting the fact 
 that certain vitreous and metallic substances likewise 
 crystallise in rhombohedra, and further, that although 
 Calcite does seem to take by preference a rhomboidal 
 figure, it takes also forms which are very different. Our 
 crystallographers, in borrowing from the geometers the 
 method by which a rhombohedron may be transformed 
 to an octahedron, a pyramid and even a lens (for there 
 is a lenticular spar), have only substituted ideal com- 
 binations for the real facts of Nature. No crystallisa- 
 tion will ever afford a specific character, for the variety 
 is infinite ; not only are there forms of crystallisation 
 common to several substances of different nature, but, 
 conversely, there are few substances of like nature 
 which do not offer different forms of crystallisation. It 
 would thus be more than precarious to establish 
 differences or resemblances, real and essential, by means 
 of this variable and almost accidental character." 
 
 The truth 27. That SO distinguished a naturalist as Buffon could de- 
 obVious. cline to recognise the correctness of the new theory is itself a 
 testimony to the difficulty of the step which had just been 
 taken. It was, indeed, not obvious on inspection that all 
 the crystalline forms of a mineral belong to one series; and 
 this is sufficiently evidenced by the discovery having been 
 postponed to the time of Rome de I'lsle. The reasons are 
 not far to seek : in the first place, as Eome de I'lsle himself 
 remarks, mineralogists had not at that time begun to collect 
 specimens conspicuous for the excellence of their crystalline 
 form, having been content with such as well displayed the 
 colour and lustre of a mineral, or the grouping of its crystals : 
 in the second place, as was noticed above in the case of Rock- 
 crystal, the symmetry of the arrangement of the angles may 
 be almost hopelessly disguised by the differences in size of the 
 corresponding faces. 
 
 * Histoire ns^turelle des Mineraux. Paris, 1783-8. 
 
34 
 
 Discovery of the importance 
 
 Haiiy's 
 discovery 
 
 of the 
 importance 
 of cleavage 
 
 Haiiy's 
 
 primitive 
 
 forms. 
 
 28. The abbd Haiiy,* however, soon broke down all opposition 
 to the new science by discovering that a certain figure of 
 the series of crystallisations has a distinct claim, if not an 
 absolute right, to recognition as the true primitive form, and 
 also that a wonderfully simple law controls the positions of the 
 secondary faces. 
 
 These important discoveries we now proceed to explain. Specimen, 
 A six-sided prism of Calcite had fallen from Haiiy's table and 
 had been broken in a way which attracted his attention : the 
 fracture instead of being irregular, like that of glass, presented 
 a smooth plane face " with Nature's polish." On trial Haiiy 
 found that, with the help of a knife, further slices could be split 
 off, not only parallel to the new face, but also in other directions 
 similarly related to the alternate edges of the prism ; and by 
 carrying on the division to a certain point, he reduced (as 
 indeed had been already done by Gahn, the pupil of Bergmann) 
 the six-sided prism to a rhombohedron. Eepeating this ex- 
 periment on other specimens of the same mineral, Hauy found 
 that, whatever the outer form, the crystal could be reduced by 
 cleavage to a kernel which always had exactly the same shape 
 and the same angles; and that, treating this kernel as the 
 primitive form, all the various crystallisations of Calcite could be 
 derived from it by the process of Romd de I'lsle explained above. 
 Extending the area of his experiments, Haiiy found that this 
 property was not peculiar to Calcite, but a general one ; whence 
 he inferred that the kernel obtained from a mineral by cleavage 
 must be regarded as its true primitive form. 
 
 29. The various kinds of primitive form obtained by him Models. 
 during a long course of investigation were the following : 
 
 Pig. 30. 
 
 1. The cube, 
 
 2. The regular octahedron, 
 
 "• Essai d'une th^orie siir la structure des crystaux. Paris, 1784. 
 
of cleavage. 
 
 35 
 
 3. The regular tetrahedron, 
 
 4. The rhombic dodecahedron (Fig. 30) ; 
 
 Fig. 31. 
 5. The rhombohedron, obtuse or acute (Fig. 31) : 
 
 Fig. 32. 
 
 6. The octahedron, with square, rectangular, or rhombic 
 base (Fig, 32) ; 
 
 Fig. 33. 
 
 7. The four-sided prism, with edges at right angles to the 
 base, the base being either a square, a rectangle, a rhomb, 
 or merely a parallelogram (Fig. 33) ; 
 
 Fig. 34. 
 
 8. The four-sided prism, with edges inclined obliquely to 
 the base, the base being either a rectangle, a rhomb, or 
 merely a parallelogram (Fig. 34) ; 
 
 c 2 
 
36 
 
 Hauys theory of 
 
 9. The regular six-sided prism (Fig. 35) ; 
 10. The double six-sided pyramid (Fig. 36). 
 
 Fig. 33. 
 
 Fig. 36. 
 
 30. Haiiy further grouped these numerous figures into dif- 
 ferent kinds in another way : 
 
 (1) Figures bounded by parallelograms (Figs. 30a, 30cZ, 
 
 31, 33, 34). 
 
 (2) Figures bounded by eight triangles (Figs. 30&, 32). 
 
 (3) The regular tetrahedron (Fig. 30e). 
 
 (4) The regular six-sided prism (Fig. 35). 
 
 (5) The double six-sided pyramid (Fig. 36). 
 
 His theory 31. By his study of cleavage Haiiy was led to frame a theory 
 of the gf ^j^g strudwre of ci-ystals, and to discover a law which connects 
 
 structure . i i » i ... 
 
 of crystals, the secondary faces with those or the primitive lorm. 
 
 He found that the kernel obtained by the cleavage of any 
 crystal can be itself split up, and apparently without limit, 
 for a plane of cleavage parallel to a face of the kernel is 
 obtained, starting from any point at which the knife is 
 placed. 
 
 Not believing in the infinite divisibility of crystals, Haiiy 
 was led to imagine that every crystal of the same substance 
 can, theoretically at least, be reduced by cleavage to minute 
 bricks of a definite size and shape, though too small to bo 
 separately visible. 
 
 32. Conversely — he argued — it must be possible from these 
 minute bricks to build up a crystal having any of the forms 
 presented by the mineral ; it is only necessary to discover 
 the mode in which the bricks must be arranged. For simplicity 
 take the case where the little bricks are cubes. 
 
 In the first place, the resulting structure is to have the 
 property of cleavage, and at all its parts the faces obtainable 
 by cleavage are to have the same directions, Hence not 
 
the s.tr net lire of crystals. 
 
 37 
 
 oaly must the cubes be arranged parallel to each other in rows 
 and layers, but they must not be interlocked, as are the bricks 
 of an ordinary wall wherein cleavage is to be specially guarded 
 against. 
 
 In the second place, the outer surface of the structure is to 
 consist of a series of plane faces. A cube of any dimensions 
 can be made still larger by adding to each of the faces layers Models. 
 of the proper size : but suppose that, starting from any edge 
 of the cube, every new layer is just one row of bricks less 
 in extent than the previous one; the layers will now be 
 arranged in regular steps ascending from this edge, and all 
 their edges will lie in a plane, just as those of a flight of 
 stairs can all be touched by a carpenter's straight-edge (Figs. 
 
 FiK. 37. 
 
 37 and 38a). But the little bricks being really too small to 
 be separately visible, the steps will appear to be wholly 
 in this plane, and will thus form a secondary face equally 
 inclined to two faces of the cube, for in each step the height 
 
 M 
 
 
 
 
 
 
 
 
 '1 
 
 
 
 
 
 
 ./.-"i 
 
 1 
 
 /_._ 
 
 
 
 
 <±-:";:: 
 
 
 J ::. 
 
 
 
 
 
 
 i 1 
 
 : _-:-X- 
 
 
 ^ 
 
 
 
 
 
 
 
 
 '_i.:__: 
 
 
 
 1 1 
 
 
 
 
 
 , 
 
 
 '"^i-- 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • |- - 
 
 
 
 
 
 
 
 
 
 
 
 ,' 
 
 
 
 "^ 
 
 ^LL 
 
 
 1 
 
 j__ 
 
 Fig. 38. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ,1 
 
 
 wl 
 
 
 is equal to the width. In the same way, a secondary face, 
 having with respect to the faces of the cube an inclina- 
 
38 
 
 The law of whole numbers. 
 
 tion different from the above, but still determinable either 
 by construction or by calculation, would be produced by the 
 regular omission of two, three or more rows, or by the 
 deposition of layers two, three or more bricks in thick- 
 ness : in Fig. 38, LM shows the inclinations of the secondary 
 face to those of the cube when each step is (a) one brick wide 
 and one brick high, (&) two bricks wide and three bricks high, 
 and (c) one brick wide and two bricks high. 
 
 If the arrangement of steps shown in Fig. 37 start from all 
 the similar edges and be similarly disposed with regard to the 
 
 Fig. 39. 
 
 similar faces of the primitive form, there will result such a group 
 of steps as is shown in Fig. 39a, and, if the bricks be too small 
 to be separately visible, such a group of faces as is shown in 
 Fig. 396: the same group can be derived from the cube by 
 the process of Eome de I'lsle (Fig. 5), as indicated in § 22. 
 
 Haiiy's law 33" ^^ ^^^ theory of Haiiy be true, it follows that the second- 
 "umbeis^ ary faces have not absolutely arbitraiy positions, as had been 
 supposed by Eome de I'lsle, but only such as would result 
 from the omission of whole numbers of rows, and from the 
 layers having a thickness measured by some multiple of that 
 of a single brick. 
 
 In fact, Haiiy proved by measurement of a vast number of 
 crystals that the inclinations of the secondary faces to those 
 of the primitive form are such as would result in this way, and 
 that the number of bricks in the width or height of a step is a 
 very simple onC) rarely exceeding six. 
 
 34. Suchj briefly stated, is Haiiy's theory of the structure of 
 
Objections to the theory of structure. 39 
 
 crystals. It is so simple, and moreover so completely consistent 
 with the results of measurement, that the existence of series of 
 crystallisations of the same mineral, all derivable according to 
 simple laws from a primitive form characteristic of the mineral, 
 was no longer questioned. 
 Objections 35. And yet the objections to the theory itself are very serious, 
 theory of ■"■* ^y °° means follows that, because a crystal may be reduced 
 structure, by cloavagc to certain fragments, the growth has taken place 
 by the grouping together of the same fragments ; and, indeed, 
 we know that in slaty rocks the direction of cleavage is 
 quite distinct from that of the planes of deposit. Again, 
 some minerals have no distinct cleavage ; others appear to be 
 distinctly cleavable only in one or two directions : and as a solid 
 figure can not be bounded by faces having fewer than three 
 directions, it is difficult to grant that in such minerals there is 
 any cleavage-kernel at all. A more serious objection still is 
 that when the cleavage-form is an octahedron, as in the case of 
 Fluor, it is impossible to arrange the constituent bricks so as to 
 completely fill up space ; in fact, that the little octahedra may 
 be parallel to each other and have their faces in directions 
 parallel to the cleavages of the resulting crystal, they have to 
 be arranged with only their angular points in contact, and it 
 is difficult to see that such a skeleton-like structure would not 
 immediately collapse. Further, the two acknowledged facts, 
 namely, the existence of series of crystallisations and the 
 dependence of the positions of the secondary faces upon whole 
 numbers, would still be explained in the same ^ay if, instead 
 of the cleavage-kernel, some other figure of the series were 
 adopted as the primitive form. 
 
 Since the time of Haiiy, the atomic theory of the constitution 
 of matter has led to a more philosophical treatment of the facts 
 which gave rise to his theory of crystalline structure. In the 
 mathematical investigations made by Bravais, and lately ex- 
 tended by Sohncke, the idea of brick-like units in actual contact 
 with each other has given place to that of atomic groups, the 
 centres of mass of the latter being imagined to be arranged in 
 the same way as the centres of the bricks of the original theory 
 — namely, in straight lines and parallel planes. These investi- 
 gations have furnished results of great interest to the student* 
 
40 Invention of axes and of 
 
 Inventionof 36. Weiss,* the Professor of Mineralogy at Berlin, was the 
 "syTtems of ^''®*' ^^ invent a mode of treatment which connected together the 
 cryataiiisa- facts without requiring the assistance of any theory of structure 
 
 tion bv ill 
 Weiss and ^^ *^'' 
 
 Mohs inde- In the first place, he arranged the primitive forms of 
 pen en y. jjj^^y jj^^.^ i^^^^ classes, cach distinguished by a purely geo- 
 metrical character. 
 
 I. By joining the centres of the opposite faces of the 
 cube, or the opposite solid angles of the regular 
 octahedron, or the three pairs of similar solid angles 
 of the rhombic dodecahedron, or the middle points of 
 opposite edges of the regular tetrahedron, he obtained 
 in each case three equal lines at right angles to each 
 other, 
 
 II. Similarly, from the octahedron or the right prism 
 with a square base, he again obtained three lines 
 at right angles, but now only two of them were of 
 equal length. 
 
 III. From a rhombohedron, or a regular six-sided prism, 
 or a double six-sided pyramid, he obtained three lines 
 in the same plane, all equal in length and equally 
 inclined to each other, and a fourth line differing from 
 the others in length and having a direction perpendi- 
 cular to their plane. 
 
 IV. From an octahedron or a four-sided prism not having 
 a square base, he obtained three lines at right angles 
 but all of different lengths. 
 
 37. Conversely, starting from these four classes of sets of 
 lines, Weiss deduced all the primitive forms of Haiiy by con- 
 structing planes which passed : — 
 i. — through ends of three lines, 
 
 ii. — through ends of two of the lines and parallel to a 
 third, 
 or iii. — through an end of one of the lines and parallel to two 
 of them. 
 
 * De indagando formarum crystallinarum charactere geometrico princlpali 
 dissertatio. Lipsiie, 1809. Uebersichtlicbe Darstellung der verschiedenen 
 naturlichen Abtheilungen der Krystallisations-systeme. (Denksch. d. Berl. 
 Ak. d. WiBsensch. 1814-15.) 
 
systems of crystallisation. 41 
 
 In other words, the planes either passed through an end of a 
 line or else wovild not meet that line at all. 
 
 38. In the second place, he found that by taking points 
 along each of these lines at twice, three times and four times, 
 &c., the original length, and constructing planes in the same 
 way as before, he obtained a set which included all those 
 secondary planes of which the actual existence on crystals 
 had been demonstrated by Haiiy. 
 
 These fundamental lines Weiss called axes. 
 
 39. A little later, but quite independently, Mohs,* the suc- 
 cessor of Werner at Freiberg, arrived by a different process 
 of reasoning at the same division into four classes, or, as Mohs 
 now called them, systems of crystallisation. 
 
 The process was identical with that of Eome de ITsle (§§ 22 
 & 23), except that the positions of the derived planes were now 
 limited by the law of whole numbers, in that the lengths cut 
 off by these planes from each one of certain lines of the 
 fundamental figure were in the ratio of whole numbers. The 
 kinds of fundamental figure, each giving rise to a separate 
 system of crystallisation, were as follows : 
 
 1. — The cube ; 
 
 2. — The octahedron with a square base ; 
 
 3. — The rhombohedron ; 
 
 4. — The octahedron with a rhombic base ; 
 and the systems of crystallisation derived from these were re- 
 spectively called the Cubic, Pyramidal, Ehombohedral, and 
 Prismatic ; they correspond exactly with the groups I., II., III., 
 IV. of Weiss. 
 
 The notion 40. The notion of a primitive form thus disappeared wholly 
 
 rrimitive ^^"'^ ^^® Crystallography of Weiss, and almost from that of 
 
 form Mohs. The latter does, in truth, appear to take a primitive 
 
 disappears, flg^jg^ \y^^ Jig employs it merely to dsjme the series, and this 
 
 * The characters of the classes, orders, genera, and species ; or, the charac- 
 teristics of the Natural History System of Mineralogy. Edinburgh, 1820. 
 Treatise on Mineralogy ; or, the Natural History of the Mineral Kingdom : 
 (translated from the German). Edinburgh, 1825. 
 
42 The idea of hemihedry. 
 
 might be done by means of any one of its figures: thus, 
 exactly the same series of planes may be derived by his pro- 
 cesses from the regular octahedron as from the cube. 
 
 The faces, which are predominant, or constantly occur, or 
 are directions of cleavage, were regarded by neither Weiss nor 
 Mohs as the origin of the series. 
 
 A simple 41. Since' all similar edges and solid angles of each funda- 
 forra. mental figure of Mohs were to be similarly altered, the existence 
 of a single derived plane necessitated, as was the case in the 
 theory of Eome de I'lsle, the simultaneous existence of a 
 number of others having definite positions ; such a set of faces 
 was called by Mohs a siinvple form of crystallisation. Thus the 
 regular octahedron, being derivable from the cube by a sijni- 
 lar alteration of all the similar solid angles, is a simple form. 
 
 A combina- If the faccs of more than one simple form are present on a 
 tion. crystal (Figs. 5-9, 11-14), the resulting compound form is 
 termed a combination. 
 
 As crystals generally exhibit combinations, and further, 
 (§§ 16 & 27) the faces which are crystallographically similar 
 usually vary considerably both in shape and size, such a series 
 of large crystals as those of Fluor and Calcite shown in the case, 
 presenting combination^, at once systematically developed and 
 not too complex to be readily intelligible to the inexperienced, 
 is one which it is difficult to get together; and indeed, the 
 visitor will probably find that the specimens in the General 
 Collection itself have usually forms which can only be 
 interpreted after a most careful study. 
 
 Hoiohedry 42. But there are sometimes found crystals presenting the 
 nfvfji.,, f^f'ss o^ ^^^ regular tetrahedron ; in other words, alternate faces 
 of the regular octahedron are suppressed. Kecognising this, 
 both Kome de I'lsle and Haiiy had regarded the regular 
 tetrahedron as a distinct kind of primitive form. 
 
 To bring such modes of development within the limits of 
 their systems, Weiss and Mohs found it necessary to imagine 
 that simple forms may not only be complete, like the octahedron, 
 but semi-complete, like the tetrahedron : the foi-mer kind was 
 termed holohedral and the latter hemihedral. The half which 
 presents itself is, however, not an arbitrary one, but can in 
 
 hemihedry. ' 
 
Tloo iieio systems of crystallisation. 43 
 
 every instance be geometrically derived in a systematic way 
 from the complete simple form. 
 
 Discovery 43. Up to the present mention has been made of only four 
 "^sllt'cmr" ^y^tems of crystallisation. In 1822 the precise measurement 
 of crystal- of Certain crystals by means of a more accurate instrument, the 
 lisation. reflective goniometer, invented in 1809 by Wollaston, led Mohs 
 to assert the existence of two additional systems ; for he found 
 that the crystals presented forms which could not be referred 
 to the kind of octahedron previously adopted, in which the 
 lines joining the three pairs of opposite angles are perpendicular 
 to each other, but must be referred to a kind of octahedron 
 in which, in one class of cases, two of these lines, and in the 
 other class of cases, all three lines, are obliquely inclined to 
 each other. Weiss, however, so strongly urged objections to 
 the recognition of the new systems, still regarding those crystal- 
 line forms merely as developments of half-forms and quarter- 
 forms from rectangular axes, that their independence can 
 only be considered to have been fully established in 1833 by 
 the discovery of the diflerent actions of these crystals on light. 
 The behaviour of minerals with regard to light is so important 
 a character, that we must here make a short digression. 
 
 ^o* 
 
 44. Up to the year 1819 no connection had been traced 
 
 between the form and the physical properties of a crystal, but 
 
 in that year Brewster discovered that the shape of the 
 
 cleavage-form is intimately related to the action of the 
 
 crystal upon light. 
 
 The optical Since 1669 it had been known that a cleavage-plate of the Specimens. 
 
 ar^a^c rs ^^g^. transparent mineral, called Iceland spar, has the strange 
 
 Iceland property of giving a double image of objects seen through it; 
 
 ^^'^^' and that a beam of light, which, for simplicity, we may regard 
 
 as entering the plate at right angles to its faces, is broken up 
 
 into two distinct beams of eqvxd brightness whatever the 
 
 position of the plate. It was further found that though the 
 
 Polarised properties of the two emergent beams are the same they are 
 
 ''^''*" distinct from those of common light, for, if either of the beams 
 
 be allowed to enter a second plate of Iceland spar, in general 
 
 two beams of vnequal brightness emerge ; when one of the 
 
44 Polarisation of light. 
 
 plates is rotated round the beam this inequality varies in 
 degree, and in four positions one or other of the beams quite 
 disappears. The beam of light thus appears to have acquired 
 " sides," and is said to be polarised. 
 
 Practically, however, it was difficult to isolate either of the 
 
 emergent beams obtained in this way, for unless the original 
 
 beam was very small, or the plate very thick, the two beams 
 
 overlapped and together produced the effect of common liglit ; 
 
 hence, for a long time, very little progress was made in the 
 
 study of the action of minerals on polarised light. 
 
 other In 1808 Malus accidentally discovered that a beam of common 
 
 obtaining ^^^^ acquires by its reflection at a particular angle from a plate 
 
 it. of glass exactly the same characters as are possessed by each 
 
 of the beams emergent from a plate of Iceland spar; and in 
 
 1813 it was discovered by Seebeck that although a beam of 
 
 common light on entering a plate of the mineral tourmaline 
 
 is resolved into two, one of them is completely absorbed if the 
 
 plate is sufficiently thick, and there emerges an isolated beam of 
 
 polarised light. 
 
 We have stated above that either of the beams, obtained by 
 arranging a plate of Iceland spar in the path of a beam of polarised 
 light, can be extinguished by giving to the plate a particular 
 position; if for the plate of Iceland spar there be substituted 
 a plate of tourmaline of the proper thickness, one of the beams 
 will, in all positions of the plate, be destroyed by the absorption, 
 and the single emergent beam, varying in brightness with the 
 position of the plate, will itself, in two positions of the plate, be 
 absolutely extinguished. Such a plate of tourmaline can thus 
 be conveniently used to ascertain whether a given beam of light 
 is common or polarised : if the light is polarised, then for certain 
 positions of the plate the beam is completely extinguished ; 
 if, on the other hand, the light is common, the emergent beam 
 is equally bright in all positions of the plate ; if the light 
 is only partially polarised, the brightness of the emergent 
 beam varies, but does not become zero, when the plate is 
 rotated round its normal. For the same purpose a plate 
 of glass inclined to the beam at a particular angle may 
 be used. 
 
 Hence a plate of glass or tourmaline can be used either as a 
 
optical characters of crystals. 
 
 45 
 
 Poiariser pohviger — foF polarisiug ordinary light, or as an analyser — 
 
 Brewster's 
 discovery 
 
 of a 
 relation 
 between 
 
 the 
 
 optical 
 
 character 
 
 and the 
 
 form of a 
 
 crystal. 
 
 analyser, for ascertaining whether or not the light is already polarised. 
 
 45. The discovery made by Malus drew the attention of the 
 scientific world to this subject, and for many years nearly all 
 its energy was concentrated on the investigation of light and 
 the alterations produced in it by minerals. At last, in 1819, 
 Brewster * was able to announce the following general laws :— 
 
 A. All transparent crystals of which the cleavage-form is a 
 
 cube, a regular octahedron or tetrahedron, or a rhombic 
 dodecahedron, are alike in being entirely without action 
 on polarised light. 
 
 B. All transparent crystals of which the cleavage-form is 
 
 a rhombohedron, a regular six-sided prism or a double 
 six-sided pyramid, an octahedron or a ^jrism with a square 
 base, are such that there is one direction, and only one, 
 in which a beam of polarised light of any colour can 
 travel through the crystal and emerge completely 
 polarised, whatever be the position of the crystal. This 
 direction depends only on the shape of the primitive 
 form ; in the prisms it is parallel to their edges, and in 
 the other figures parallel to the line joining the pair of 
 similar solid angles. 
 
 C. All crystals of which the cleavage-form is other than 
 
 the above are such that there are two, and only two, 
 directions in which a beam of polarised light of a given 
 colour can travel without alteration ; and these two 
 directions are closely related to the shape of the 
 cleavage-kernel. These directions have been called 
 optic axes. 
 
 The 46, The simplest way of rendering evident these characters is 
 
 P^ncett^"* the following : — Between two plates of tourmaline so disposed 
 
 that no light can pass through the pair, is placed a slice of the Specin 
 crystal to be examined, and the whole apparatus arranged close 
 to the eye, so that light which has passed in various directions 
 
 * On the connection between the Primitive Forms of Crystals and the 
 Number of their Axes of Double Refraction : two memoirs. (Proceedings of 
 the Wemerian Society. Edinburgh, 1821.) 
 
46 
 
 Brewster's laws. 
 
 through the slice can be at the same time observed. If the 
 slice is that of a crystal belonging to Class A, its introduction 
 between the two tourmalines produces absolutely no change, 
 and the field of view remains dark. If the crystal belongs to 
 Class B, and the faces of the slice are at right angles to the 
 direction along which polarised light can travel without 
 alteration, there will be seen a series of coloured circular rings 
 intersected by a black cross, and the appearance will be un- 
 
 Fig. 40. 
 
 changed as the slice is turned round its normal (Fig. 40). If the 
 crystal belongs to Class C, and the faces of the slice are at right 
 angles to a line equally dividing one of the angles between the 
 two directions in which polarised light of a given colour can 
 travel without alteration, the field of view remains dark at 
 two points, around each of which is a set of coloured rings. 
 
 Fig. 41. 
 
 as shown in Fig. 41. In four positions of the slice the 
 rings are seen to be intersected by a dark cross, but in other 
 positions the dark cross breaks up into two dark bands, termed 
 brushes, each passing through the centre of one of the sets of 
 rings, which, it, may be added, appear to move with the crystal 
 during its rotation. 
 
Only six systems are possible. 47 
 
 Agreement 47. This division of crystals into classes according to their 
 
 optfcafand Optical behavlour is in perfect agreement, as far as it goes, with 
 
 geometrical that which had just before, on geometrical grounds, been 
 
 cL"^fying suggested in Germany by Weiss and Mohs, and of which 
 
 crystalline Brewster had not at that time heard ; the only difference being 
 
 °'^™ ■ that optically no distinction could be made between crystals 
 
 belonging to the systems termed Pyramidal and Ehombohedral 
 
 by Mohs. Still, Brewster's discovery was quite sufficient to 
 
 prove that the grouping suggested by Weiss and Mohs is a 
 
 natural one, depending on fundamental differences of structure. 
 
 Optical 48. We have already stated (§ 43) that Mohs afterwards 
 
 '''ofHhr^ (1822) recognised two additional systems, the crystals belonging 
 
 crystals to which Weiss and himself had previously regarded as merely 
 
 h^ been developments of half-forms and quarter-forms belonging to the 
 
 referred to Prismatic system. The independence of these systems was 
 
 systons!"^ at length confirmed by the difference in the optical characters 
 
 of the crystals assigned to them. 
 
 In those crystals, which both Weiss and Mohs regarded as 
 undoubtedly belonging to the Prismatic system, the two lines 
 which bisect the angles between the optic axes, and a third line 
 at right angles to both of them, were proved to be identical in 
 direction with the three lines which, on geometrical grounds, 
 had been selected for crystallographic axes, and they were also 
 found to be independent both of the colom* of the light and the 
 temperature of the crystal. On the other hand, in the fifth 
 system of Mohs two of these lines, and in the sixth system 
 all three, were found to be quite distinct from the rect- 
 angular crystallographic axes adopted by Weiss, and to vary 
 in position in the crystal, not only with the colour of the light, 
 but also with the temperature at which the observations were 
 made. 
 There can- 49. The fundamental character of each of these six natural 
 not be more gygtems is now regarded as one of symmetry ; in a crystal belong- 
 systems. Ing to the Prismatic system of Mohs, for instance, every feature, 
 whether geometrical or physical, is repeated in directions 
 symmetrically disposed on opposite sides of three rectangular 
 planes. And one of the most remarkable discoveries of the last 
 half-century has been the mathematical demonstration, that 
 
48 Distinction of minerals into kinds. 
 
 if the law of whole numbers enunciated by Haiiy be absolutely 
 true, these six kinds of symmetry, and no others, are possible 
 in ciystals. 
 
 The 50. We have now indicated the steps by which it has been 
 
 of minerals '^^0'*^^ '^^^ substanccs of " the Same kind " crystallise in forma 
 into kinds, which are intimately related to each other, and are capable of 
 reference to one or other of six natural systems. 
 
 In case aii exception to this general law presents itself, it is 
 necessary, in the first place, to ascertain whether the exception 
 is not an apparent one, for it is possible that the substances 
 may really not belong to the same kind. For instance, in the 
 case of the specimens which had up to his time been called 
 Heavy spar, Haiiy discovered that, although the crystals from 
 England and Sicily are very similar in form, those of one Specimens. 
 locality differ in their fundamental angles from those of the 
 other by amounts not large, but yet beyond the possible errors 
 of measurement. This exception, which long puzzled Haiiy, 
 was to his delight removed by the discovery made by Vauquelin, 
 that the crystals really belong to two distinct kinds of mineral 
 (now called Barytes and Celestine respectively), one of them, 
 the English, giving a green, and the other, the Sicilian, a crimson 
 colour to a flame. 
 
 51. The difficulty as to when two specimens are to be regarded 
 as being of the same kind has so far, for the sake of simplicity, 
 been left out of sight ; and we have assumed that, somehow or 
 other, by lielp of the more obvious properties already mentioned 
 (§ 12), a discrimination into kinds can be made. 
 
 Before proceeding further it is necessary to treat with some 
 detail of a very important class of properties, distinct from the 
 rest in that their determination involves the destruction of the 
 part actually tested ; if any logical inference as to the con- 
 currence of a group of properties in an individual is to be 
 made, all the other properties must be first determined. 
 
 52. The action of fire upon a simple substance or on a mixture 
 of substances, and the action of substances upon each other, 
 
Discovery of various solvents. 49 
 
 must have been a subject of inquiry in the earliest times (§ 12), 
 one object of desire being the production of a substance more 
 valuable than those destroyed in the process. It was thus 
 discovered that lead can be got by roasting one kind of 
 mineral (galena) with charcoal ; a second mineral (tin-stone) 
 yields tin ; from a third (magnetite) iron can be obtained ; a 
 fourth (cinnabar or vermilion), when rubbed with vinegar in a 
 brass vessel, according to Theophrastus, yields quicksilver. 
 Such properties are clearly of great importance for the dis- 
 tinction of minerals into kinds. 
 DifiFerent 53. Several liquids similar to vinegar in having a sour taste 
 soiraits ^°<i ^ power of dissolving many substances insoluble in water 
 prepared, itself, wcro discovcred by the old alchemists in their search 
 for the philosopher's stone and the elixir of life ; these liquids 
 were called cmAs. 
 
 Thus, when a certain mineral (iron pyrites) after ^eing 
 roasted or slowly acted upon by the air is treated with water, 
 the resulting liquid yields, on evaporation, a solid termed " green 
 vitriol;" from this, by heating in a retort, a very powerful 
 acid, oil of vitriol (fuming sulphuric acid), was obtained. 
 
 By heating together a mixture of saltpetre and " blue vitriol," 
 another acid, cLqiui fortis (nitric acid), useful for separating 
 silver from gold, was produced. 
 
 In a similar way, from a mixture of nitre, sal-ammoniac, and 
 green vitriol, the alchemists prepared aqua regia, a liquid capable 
 of dissolving even gold itself. 
 
 And in the fifteenth century another acid, spirits of salt 
 (hydrochloric acid), was obtained by heating common salt with 
 oil of vitriol. 
 
 The difference of action of each of these liquids on the 
 products belonging to the Mineral Kingdom supplied many 
 tests by which substances very similar in their external 
 characters could be distinguished from each other. 
 
 AlkslieB. 54. By boiling in water the ashes of plants and evaporating 
 the liquid thus obtained, a substance called alkali, having 
 peculiar characters, was prepared ; and a similar substance was 
 derived from bones and other animal matters by dry distillation : 
 it was found that the latter could be distinguished from the 
 
50 Alkalies^ acids and salts. 
 
 former, not only by its pungent smell, but by the action of 
 heat, for it could be completely conyerted into vapour ; hence 
 the two kinds of alkali were termed fixed and volatile, re- 
 spectively. Later, differences of character between the alkali 
 of land-plants and that of sea-plants were observed, for the 
 colour given to the flame of a spirit-lamp by the former was 
 violet, whilst that given by the latter was yellow; the two 
 kinds of fixed alkali were 'designated potash and soda. 
 
 By being boiled with quicklime, the alkalies acquire characters 
 more pronounced than those they at first possess ; the two states 
 of the alkali were distinguished as caustic and mUd, re- 
 spectively. 
 Opposition 55_ Jq properties the alkalies were found to be opposite to 
 alkalies and the acids : they destroy both the sour taste and the solvent 
 
 acids, power; and whereas the acids turn certain blue vegetable 
 colouring matter to red, the alkalies restore the original colour. 
 
 Salts. 56_ When the solvent power of an acid was neutralised or 
 
 destroyed by the action of a metal, an alkali or an earth, 
 
 another kind of substance called a salt was produced. 
 
 Alkaline 57_ _^tout the middle of last century it was remarked that 
 
 lime, a substance known to the ancients, had similar properties 
 
 to those of the alkalies; owing to its being almost insoluble 
 
 in water and to its remaining unaltered when exposed to a high 
 
 temperature, it had been long regarded as one of the " earths ; " 
 
 it was now termed an alkaHne earth. Other similar earths, 
 
 magnesia, baryta and strontia, were soon afterwards distinguished. 
 
 58. About this time it was discovered that gases, invisible 
 
 but yet having very different properties, could be prepared. 
 
 Different The gas evolvcd when limestone was acted upon by an acid 
 
 "as" was found to be distinct from common air, and was termed 
 recognised, fixed air (carbouic acid) ; another gas (oxygen), given off when 
 a certain substance was heated, was found to have very energetic 
 properties ; common air was found to be a mixture of the 
 latter with still another gas (nitrogen) ; a fourth gas (hydrogen), 
 light and inflammable, was obtained by treating iron filings 
 with dilute oil of vitriol: water was shown to be composed 
 of two of these gases (hydrogen and oxygen). 
 
 A new 59_ ^ theory was now proposed which was to account for the 
 
 theory* peculiarities which had been discovered. The metals, long re- 
 
Daltoiis atomic theory. .01 
 
 garded as compounds and as capable of being changed one into 
 another, are, according to the new theory, elements incapable 
 of resolution into simpler substances ; to this class were also 
 assigned some non-metallic substances, such as sulphur, phos- 
 phorus and carbon, and some of the lately discovered gases 
 (hydrogen, oxygen and nitrogen) : the number of elements then 
 known was only twenty-three. All other kinds of matter were 
 considered to be compounds of the elements with each other. 
 By reason of the facility with which it enters into combination 
 with the other elements, and its influence over the characters 
 of the resulting compounds, oxygen was regarded as the most 
 important of the simple substances. In general its compounds 
 with non-metaUie elements are acids, and its compounds with 
 metals are hoses or substances which have the property of 
 neutralising acids : according to the same theory, a salt is 
 produced by the imion of an acid with a base. 
 The law of 60. The ucxt step was the discovery that every distinct 
 tb™i ™de- chemical compound always contains exactly the same proportion 
 finite pro- of the elements of which it is composed ; a fact first indicated by 
 po ions. ^^ experiments made by Cavendish with neutral salts, for he 
 showed that in these compounds the proportion of base 
 to acid obeys a distinct law ; this view, however, was stoutly 
 opposed by Bertbollet, and it was not till 1808 that the fact 
 was conclusively established by the researches of Proust. 
 The atomic 61. About this time Dalton announced his atomic theory, 
 theory. Af^^rding to this theory there are in Nature different kinds of 
 minute indivisible particles, which Dalton called atoms; all 
 atoms of the same kind are the same in figure and in weight ; 
 each elementary body consists of only one kind of atom; 
 atoms of different kinds are capable of combining together in 
 simple proportions to form small groups ; a definite chemical 
 compound consists of a collection of such atomic combinations, 
 all of exactly the same kind. 
 
 The long series of investigations made by Berzelius (and 
 more recently by Stas) to determine with accuracy the relative 
 weights of the different kinds of atom, rendered it so clear 
 that the proportions by weight in which the elements combine 
 to form definite chemical compounds are fixed, that this 
 constancy is now scarcely called in question. 
 
 D 2 
 
52 Chemical composition of minerals. 
 
 Have 62. But is a mineral a definite chemical compound? To 
 
 ™f thV Hauy,* in 1801, this question presented serious difficulties ; 
 
 same kind and in his Treatise he refers to Felspar as an illustration. 
 
 "chei^oai Kirwan had brought together analyses of thirteen different 
 
 composi- specimens which had all been called Felspar, and to these Hauy 
 
 ■ adds an analysis made by Vauquelin of a fourteenth specimen. 
 
 The results varied extremely, for not only were the proportions 
 
 of the various constituents not constant, but one constituent 
 
 present in considerable quantity in some of the specimens was 
 
 entirely absent from the rest. Hence, Hauy was led to criticise 
 
 the grounds upon which these specimens had been named 
 
 Felspar ; they were as follows : — (1) the specimens were so hard 
 
 that they gave sparks when struck with steel ; (2) they yielded 
 
 rhomboidal fragments when broken ; (3) they were about two 
 
 and a half times as heavy as water ; (4) they were fusible and 
 
 gave a white bead. 
 
 Haiiy contended that such properties were not sufficiently 
 definite and precise to serve for the distinction of minerals into 
 kinds {species) ; he therefore recommended that, in the distri- 
 bution of minerals into kinds attention should be paid to the 
 crystalline form, and that specimens should not be regarded 
 as belonging to the same kind of mineral unless their crystals 
 presented the same primitive form. Haiiy ventured to assert that 
 when this limitation was introduced all minerals of the same 
 kind would be found to have essentially the same chemical com- 
 position, for he could not believe that the little " bricks " could 
 have exactly the same form without being of identical chemical 
 constitution ; except where the primitive form is a cube, regular 
 octahedron or tetrahedron, and has thus an absolutely definite 
 shape, 
 
 63. Yet Haiiy perceived that even where the primitive form is 
 the same there is still much variation in the chemical com- 
 position of minerals ; and this difficulty he sought- to explain in 
 the following ingenious but artificial way. At Fontainebleau are 
 found crystals of Calcite, which have as much as from 50 to 60 per 
 cent, by weight of sand grainsdisseminated through them, and 
 
 * Traitd de Mineralogie. Paris, 1801. 
 
Dimorphism and Triniorphism. 53 
 
 yet have the same shape of cleavage-kernel as the pure mineral ; 
 from the fact that this large proportion of mingled foreign 
 matter has failed to influence the angles of the crystals built 
 up from the little bricks of Calcite, Haiiy argued that the 
 variations of chemical composition of minerals, which otherwise 
 appear to be of the same kind, are due to the interposition of 
 foreign matter between those constituent particles to which the 
 form of the crystal is really due. 
 
 64. The presence of this foreign matter would, according to 
 Haiiy, at the same time account for the variations of colour, and 
 for the slight differences of hardness, fusibility and other charac- 
 ters, met with in specimens regarded as belonging to the same 
 kind of mineral. According to this theory, Dolomite, Chalybite Specimens. 
 and Bitterspar are all varieties of Calcite, the large differences 
 of composition being due to the interposition of carbonates of 
 magnesia or iron between the particles of carbonate of lime, of 
 which the extraordinary crystallising power was supposed to be 
 demonstrated by the Fontainebleau crystals. 
 Di- 65. Haiiy thus acknowledged that, in the Mineral Kingdom, 
 
 "ncftri™ crystals having the same primitive' form and a general simi- 
 morphism. larity of character may have a very different chemical com- 
 position. On the other hand, he found that, in at least one 
 case, crystals yielding a different primitive form have the same Specimens 
 percentage chemical composition ; for while one kind of 
 carbonate of lime (calcite) can, as we have seen, be reduced by 
 cleavage to a rhombohedron, a second kind (aragonite), when 
 cleaved, yields an octahedron ; this character has been termed 
 dimorphism* To those who thence argued that his theory of the 
 association of a definite primitive form with a definite chemical 
 composition must be founded on wrong premises, Haiiy replied 
 that at any rate he could not regard two specimens as belonging 
 to the same kind of mineral merely because they had one single 
 property in common, namely, identity of chemical composi- 
 tion ; that the difference of primitive form was, in the case of 
 calcite and aragonite, as also in that of diamond and graphite, 
 associated with differences of hardness, density, and all the 
 other properties, save chemical composition ; and that there was 
 
 " Di-, doubly, and morplie, form. 
 
54 Discovery of the law of isomorphism. 
 
 no exception to the more general law that a definite primitive 
 form is allied with a definite set of properties. 
 
 To remove this exception to the generality of Haiiy's theory, 
 countless specimens of aragonite were analysed with the view 
 of discovering some constituent other than carbonate of lime, 
 and it was vainly hoped by some, though not by Haiiy himself, 
 that the presence of carbonate of strontium, small quantities of 
 which had been found in some isolated specimens, might 
 be held to account for the difference — an explanation which 
 would require the traces of carbonate of strontium to have such 
 a tremendous power of crystaUisation as to completely over- 
 come even that of the carbonate of lime. 
 
 In 1822-3 Mitscherlich announced another exception, and 
 showed that while crystals of sulphur deposited from solution 
 have one kind of primitive form, those obtained by allowing 
 melted sulphur to quickly cool have a different one. 
 
 By the conversion of aragonite into calcite, and again by the 
 production of both from the same solution, it was eventually 
 made clear that the difference of form, to whatever due, can 
 not be rightly attributed to slight difference in the chemical 
 composition. 
 
 Later still (1845), it was shown that titanic acid is trimorj^hous, 
 appearing in Nature with three distinct primitive forms, each 
 connected with a definite, but different, set of properties. 
 ^T. 66. To Mitscherlich* belongs the credit of establishing 
 
 the existence, not only oi artificial crystals havmg the same 
 chemical composition and different primitive forms (dimor- 
 phism), but also of others having the same primitive form and 
 essentially different chemical compositions, a character termed 
 isomorpMsm.'\ This discovery followed from the examination 
 of a series of phosphates and arsenates of the alkalies, artificial 
 salts of which the purity could be secured. From his inves- 
 tigations Mitscherlich inferred that the chemical elements may 
 be distributed into sets, the members of each of which are so 
 far similar to each other that, in a chemical compound, one 
 
 • Ueber das Verhaltniss der Krystallfonn zu den chemiBchen Proportionen. 
 Uel)er die Korper welche in zwei verschiedenen Formen crystallisiren, 
 (Abhandl. d. Berl. Ak. d. Wissenscb, 1822-3.) 
 
 ■f Isos, equal, and morplie, form. 
 
Systems of classification. 55 
 
 atom can replace another atom of the same set without 
 appreciably affecting the primitive form of the crystal. 
 Potassium and sodium belong to one of these sets ; phosphorus, 
 arsenic and antimony to another. He also inferred that the 
 crystalline form of a chemical compound depends, not only on 
 the percentage composition, but also on the configuration of the 
 atomic groups. 
 
 67. The discovery of isomorphism in artificial salts removed 
 the great difficulty presented by the fact that, in the Mineral 
 Kingdom, crystals may be different in chemical composition, 
 and yet so similar in form and general characters that they can 
 scarcely be regarded as belonging to different kinds of mineral ; 
 for it indicated that although there is not in these crystals 
 that absolute identity of matter which Haiiy had been led to 
 expect, still there is an identity of grouping of atoms and a 
 law controlling the replacement of the members of the groups. 
 
 Systems of 68. Having glanced at the more important properties, by 
 tion. help of which Minerals are distributed into kinds or species, we 
 must next briefly consider how the kinds are to be classified, 
 and thus how we are to ascertain readily whether or not a new 
 specimen, of which the characters have been determined, is 
 similar to some one of the many already described. The great 
 discoveries made in crystallography and chemistry during the 
 latter part of the last century render it unnecessary to discuss 
 the classifications employed in earlier times. 
 
 Berzelius. 69. Berzelius* (1815) was the first to frame a system of 
 classification depending only on chemical composition. The 
 study of electricity had given rise to a theory that the act of 
 chemical combination is an electrical phenomenon ; and th^t 
 every chemical compound consists of two parts, the one electro- 
 positive (the metal), the other electronegative (the acid). In his 
 system, Berzelius brought together into one family all chemical 
 compounds having the same electropositive part (the metal), and 
 arranged the families among themselves according to the degree 
 of the electropositivity of the metal : each family was distributed 
 into orders arranged according to the degree of electronegativity 
 of the acid part of the compound. 
 
 * Forsok till ett rent kemiskt Mineralsystem. Stockholm, 1815. 
 
56 A Natural History system 
 
 The arbitrary nature of this system was made manifest by 
 the discovery of isomorphism by Mitscherlich, according to which 
 elements extremely different in electrochemical character can 
 replace each other without appreciably affecting the characters 
 of the compoimd. Berzelius thereupon acknowledged the com- 
 pleteness of his failure and reconstructed a chemical system 
 (1824), depending now on the electronegative part (the acid) : 
 but to this, though more satisfactory in its results, the same 
 objection may be urged, namely that the properties of a mineral 
 have no manifest connection with the electrochemical character 
 of its constituents. 
 Mohs, 70. About the same time (1820), Mohs * framed a " Natural 
 History system of classification," wherefrom the chemical 
 composition of a mineral was completely excluded as not being 
 a "Natural History" property, since it could only be deter- 
 mined by destroying the part of the mineral experimented 
 upon. As this system of classification was adopted, more 
 especially in Germany, for many years, and has had great 
 influence on the progress of mineralogical science, a brief 
 statement of its leading features will not be out of place. 
 
 In framing the system, account was taken, not of a smgle 
 character, but of all the more important of the external (or 
 Natural History) characters, the most prominent in the defini- 
 tion of species being crystalline form (including cleavage), 
 hardness and specific gravity. 
 
 The first of these has a definite geometrical significance, 
 and the last has a definite numerical value : to give a 
 similar precision to the character of hardness, Mohs con- 
 structed an arbitrary scale by means of ten minerals, of 
 which experience had proved the suitability for the purpose ; 
 the minerals, in the order of increasing hardness, were : — 
 
 1. Talc. 
 
 6. Adularia. 
 
 2. Eock-salt. 
 
 7. Eock-crystal. 
 
 3. Calcite. 
 
 8. Topaz. 
 
 4. Fluor. 
 
 9. Corundum. 
 
 5. Asparagus-stone. 
 
 10. Diamond. 
 
 * The characters of the classes, orders, genera, and species; or, the 
 characteristics of the Natural History System of Mineralogy. Edinburgh, 
 1820. 
 
of classification. 57 
 
 For the sake of brsTity, the degree of hardness was ex- 
 pressed numerically ; a specimen, for instance, which was 
 estimated to be scratched as easily by Fluor as Calcite by 
 the specimen itself, was said to have a hardness 3 "5. 
 According to the system of Mohs, the number of classes of 
 the Simple Minerals is three, of which the characters are as 
 follows : — 
 
 Class I. Specific gravity under 3 ■ 8 : no bituminous odour : 
 if solid, a taste. 
 
 Class II. Specific gravity above 1 • 8 : tasteless. 
 Class III. Specific gravity imder 1 • 8 : a bituminous odour : 
 if solid, tasteless. 
 
 As few minerals have so low a specific gravity as 1*8 or 
 have a taste, the second class includes nearly the whole of the 
 kingdom, the first consisting, almost solely, of the minerals 
 which are soluble in water, and the last, of the organic 
 products resin and coal. 
 
 In Class II. are recognised thirteen orders, designated by 
 the following names : — 
 
 1. 
 
 TTaTiOIDe. 
 
 5. Mica, 
 
 9. Metal. 
 
 2. 
 
 Babyte. 
 
 6. Spae. 
 
 10. Pyeites. 
 
 3. 
 
 Keeate. 
 
 7. Gem. 
 
 11. Glance. 
 
 4. 
 
 Malachite. 
 
 8. Oee. 
 13. Sulphur. 
 
 12. Blende. 
 
 Each of the orders, again, is distinguished by a comMnation of 
 characters : thus, the characters of the order Babyte are 
 
 Lustre: non-metallic. 
 
 Streak : uncoloured or orange-yellow. 
 
 Hardness : 2 '5 to 5*0. 
 
 Specific gravity : 3 ■ 3 to 7 " 3. 
 
 Further, in this order, the characters are inter-related as 
 follows : — 
 
 1. If the most distinct cleavage has only a single direction, 
 the hardness does not lie between 4 and 5. 
 
 2. If the lustre is adamantine or imperfect-metallic,, the 
 specific-gravity is not less than 5, 
 
 8. If the streak is orange-yellow, the specific gravity is 
 at least 6. 
 
58 Mohs' scientific nomenclature. 
 
 4. If the hardness is 5, the specific gravity is under 4*5. 
 
 5. K the hardness is 5 and the specific gravity is under 4, 
 the cleavage is diprismatic. 
 
 The orders are, in turn, distributed into genera, the number 
 of the latter in the order Babttb being six, termed re- 
 spectively : — 
 
 1. Parachrose-baryte. 
 
 2. Zinc-baryte. 
 
 3. Scheelium-baryte. 
 
 4. Hal-baryte. 
 
 5. Lead-baryte. 
 
 6. Antimony-baryte. 
 The characters of the genus Hal-baryte, for example, are : — 
 
 System of crystallisation : orthorhombric. 
 Hardness : 3 • — 3 • 5. 
 Specific gravity : 3 • 6 — 4- 7. 
 Finally, the genera are subdivided into species : the genus 
 Hal-baryte, for instance, contains four species, designated by 
 
 1. Peritomous hal-la/ryte, 
 
 2. Diprismatic hal-haryte, 
 
 3. Prismatic hal-la/ryte, 
 
 4. Prismatoidal hal-baryte ; 
 they are the species known as Strontianite, Witherite, Barytes, 
 and Celestine, respectively. 
 
 The above is perhaps sufiScient both to render evident the 
 difficulty of assigning a relative importance to the various 
 external characters of minerals, and to illustrate the compli- 
 cated and artificial character of the groups of properties defining 
 the orders recognised in the system of Mohs : at the same time 
 it serves to give an idea of the scientific nomenclature which 
 Mohs sought to introduce for the mineral species. 
 
 71. The system which was adopted by Professor Maskelyne 
 Kosr for the classification of the British Museum Collection is 
 virtually one published by Gustav Eose,* in 1852, as an 
 improvement on the purely chemical system, and has been 
 briefly described as a chemical system modified by the prin- 
 ciple of isomorphism : it is therefore a mixed system, depend- 
 * Das Krystallo-chemische MineralsyHtem. Leipzig, 1882. 
 
 Gustav 
 
A crystallo-chemical system. 59 
 
 ing on two properties, chemical composition and crystalline 
 fonn. 
 
 In this system minerals are arranged in four principal 
 diyisions, of which the first includes the native elements, and 
 the remaining three, the compounds. 
 
 The chemical elements most useful in the classification of the 
 compounds met with in the Mineral Kingdom are : — 
 
 (1) The Arsenic group : — arsenic, antimony and bismuth. 
 
 (2) The Sulphur group : — sulphur, selenium and tellurium. 
 
 (3) The Chlorine group: — chlorine, bromine, iodine and 
 fluorine. 
 
 (4) Oxygen. 
 
 The second division comprises those minerals in which 
 metals are combined with elements of the Arsenic and Sulphur 
 groups : the third division, those in which metals are com- 
 bined with the elements of the Chlorine group; and the 
 fourth, the compounds of Oxygen. 
 
 The divisions are subdivided into sections, and the sections 
 into classes, the latter embracing the minerals which fall 
 under the same chemical denomination ; as, for instance, the 
 gaits of the same acid or of a group of acids chemically and 
 crystallographically equivalent to each other. 
 
 Each class is further separated into distinct chemical series, 
 the minerals included in any series being such as are designated 
 by the same equivalent typical fonnula. 
 
 Finally, the chemical series are distributed into distinct 
 crystaUographic series, arranged according to the crystalline 
 systems to which they belong; these are followed by the 
 amorphous substances, which present either no crystalline 
 forms at aU, or only such as cannot be determined. 
 
 The accompanying table will serve to give a clearer idea of 
 this system : further detail will be given later in describing the 
 General Collection : — 
 
60 The System of Classification 
 
 adopted in the Mineral Gallery, 
 
 
 Hi 
 
 Div. I. JTative elements. 
 
 (The compounds 
 of metals with 
 elements of the 
 arsenic and snl- 
 phnr groups. 
 
 c The oomponnds 
 nitr Trr Jo' metals with 
 ^'^•"^•Selementsof the 
 
 (.chlorine group. 
 
 . jY i ^^ Compounds 
 
 r oxygen. 
 
 Supplement. 
 
 Sec. (1). Metallic. 
 
 Sec.' (2). Non-metallic. 
 
 Sec, (1). Absbnides, &c. 
 
 Sec. (2). Sulphides, &c. 
 
 Sec. (3). Absenosulfhides, &c. 
 
 See. (4), Sin.PHDE-SAM'S. 
 
 Sec. (1). Simple Chlobides, &c. 
 
 Sec. (2). CoMPOuHD Chlobides, &c. 
 
 Sec. (1). Oxides. 
 
 I CUisa 
 
 \ a. Carbonates. 
 
 • &. Silicates, &c. 
 
 Sec. (2). I c. MolybdatesandTvmgstates, 
 
 Oxygen i d. Chromates and Sulphates. 
 
 Salts. \ e. Borates. 
 
 • /. Nitrates; 
 
 I g. Phosphates, Arsenates and 
 I Vanadates. 
 
 Obganic Pbodbcts. 
 
( 61 ) 
 
 THE CHARACTERS OF MINERALS. 
 
 ' In window-cases II. III. and IV. is arranged a series of 
 specimens illustrating at once the characters of minerals and 
 the terms used in their description : with the view of reminding 
 the student of their existence, characters are specified even 
 when they require experiment for their determination, and are 
 thus not evident from mere inspection of the minerals as they 
 lie in the cases. The names of the illustrative minerals are 
 given in italics. 
 
 The specimens in window-case II. relate almost entirely to 
 the Forms presented by minerals. 
 
 The Forms of Crystals. Window- 
 
 The six kinds of symmeteioal distribution op the faces : — '^'° "■ 
 The Cubic (or Tesseral) system : Jluor. 
 The Tetragonal (or Pyramidal) system : apophyllite. 
 The Ehombohedral (or Hexagonal) system : ealcite, emerald. 
 The Orthorhombic (or Prismatic) system : topaz. 
 The Oblique (or Monoclinic) system : orthoclase. 
 The Anorthic (or Triclinic) system : axinite. 
 DiMOEPHiSM : — fyrites and marcasite. 
 Trimokphism : — rutile, amatase and hrookite. 
 Isomorphism : — chalybite and dolomite. 
 
 tquartz, ealcite, and quartz with the form 
 
 of ealcite. 
 I galena, pyromorphite, and galena with the 
 form oi pyromoT'phite. 
 
 Pseudomorphism : — i 
 
 Forms depending merely on the relative sizes op the 
 
 FACES : — 
 
 Prismatic (long) : epidote^ 
 Prismatic (short) : pyrosmalite. 
 Stout : apophyllite. 
 
 Slender : scoleeite. 
 
 Aciciilar : cerussite. 
 
 Capillary : millerite. 
 
 Tabular (thick) : larytes. 
 Tabular (thin) : speoulariron , 
 
62 Indeterminate forms, &c. 
 
 The Surface of Crystals ;— Window- 
 
 Smooth : pm". "^'^ "• 
 
 Drusy : qmniz. 
 
 Bough : eahite. 
 
 Striated : blende, magnetite. 
 
 Curved : calcite, dolomite^ 
 
 The Regular Growths of Crystals (twins) : — 
 Caleite, easdterite, fluor, gi/psmn. 
 
 Groups of Crystals : — 
 Parallel : quartz. 
 
 Badiating (or divergent) : mesoUte. 
 Matted (reticulated or interlaced) : chaleotrichite. 
 Confused : seofoUte, leryl. 
 
 Indeterminate forms (due to aggregation) : — 
 Globular : blende, prehnite, calcite, marcasite. 
 Branched (arborescent or dendritic) : silver, copper, 
 
 pyrolusite. 
 Dentiform : copper. 
 
 Mossy : copper. 
 
 ' Leafy : siher, gold. 
 
 Wiry (or filiform) : silver. 
 Capillary : millerite. 
 
 Coralloidal : aragomte. 
 
 Mammillary : arsenic, psilomelane. 
 
 Warty : menilite. 
 
 Nodular : blende, malachite. 
 
 Botryoidal : hyd/rodohmite. 
 
 Beniform : msnilite. 
 
 Amygdaloid al : aragonite, agate. 
 Geode : quartz. 
 
 Stalactitic : eahite, chalcedony, pyrites, psilomelane. 
 
 Amorphous : websterite. 
 
Scale of colours. 
 
 63 
 
 In window-case III. are collected together specimens illus- Window- 
 trative of those characters of minerals which relate to Light. '^"'^ ' 
 
 The Scale of Colours (suggested by Werner in 1774) : — 
 
 METALLIC COLOUES. 
 
 Copper-red : copper. 
 
 pyrites. 
 
 copper-pyrites. 
 
 gold. 
 
 Light-brass-yellow : 
 Dark-brass-yellow : 
 Gold-yellow : 
 
 Silver-white : 
 Silver-white, passing into grey : mispickel. 
 Silver-white, passing into red : eohalt-glcmce. 
 Tin-white : • antimony. 
 
 Whitish lead-grey : 
 Pure lead-grey : 
 Blackish lead-grey : 
 Steel-grey : 
 
 Iron-black : 
 
 stibnite. 
 galena, 
 nagyagite. 
 platinum. 
 
 franklindte. 
 
 NON-METALLIC COLOUES. 
 
 White. 
 
 Snow-white : 
 Eeddish-white : 
 Yellowish-white : 
 Greyish-white : 
 Greenish-white : 
 Milk-white : 
 
 Bluish-grey : 
 Pearl-grey : 
 Smoke-grey : 
 Greenish-grey : 
 YeUowish-grey ; 
 Ash-grey ; 
 
 Gket. 
 
 aragonite. 
 
 margarite. 
 
 rock-milk. 
 
 marble. 
 
 tremolite, 
 
 opal. 
 
 fluor (massive). 
 
 perlite. 
 
 flint. 
 
 hornst&m. 
 
 pearlspar, 
 
 zoisite. 
 
64 
 
 Scale of colours. 
 
 Black. 
 
 Greyish-black : 
 Velvet-black : 
 Greenish-black : 
 Brownish-black ; 
 Bluish-black : 
 
 Blackish-blue : 
 Azure-blue : 
 Violet-blue : 
 Lavender-blue : 
 Plum-blue : 
 Prussian-blue : 
 Smalt-blue : 
 Indigo-blue : 
 Duck-blue : 
 Sky-blue : 
 
 Verdigris-green : 
 Celandine-green : 
 Mountain-green : 
 Leek-green : 
 Emerald-green : 
 Apple-green : 
 Grass-green : 
 Pistachio-green : 
 Asparagus-green : 
 Blackish-green : 
 Olive-green : 
 Oil-green : 
 Siskin-green : 
 
 Sulphur-yellow : 
 Straw-yellow : 
 Wax-yellow : 
 Honey-yellow : 
 Lemon-yellow : 
 
 Green. 
 
 lycUa/n-stone. 
 towrmaline. 
 cmgite. 
 lievrite, 
 cobalt ochre. 
 
 Blue. 
 
 chessylite. 
 
 lapis laztdi. 
 
 fiuor. 
 
 teratoUte. 
 
 jluor. 
 
 salt. 
 
 chalcedony. 
 
 viviardte, 
 
 anhydrite. 
 
 lirocomte. 
 
 nowmeaite. 
 
 jasper. 
 
 heryl. 
 
 prase. 
 
 emerald. 
 
 chrysoprase. 
 
 cuprowranite. 
 
 epidote. 
 
 asparagus stone. 
 
 olivenite. 
 
 pyromorphite. 
 
 heryl. 
 
 cdkowranite. 
 
 Yellow. 
 
 svlphwr. 
 
 carplioUte. 
 
 mimetesite. 
 
 amber. 
 
 orpimeni. 
 
 VlTindow- 
 caae III. 
 
Scale of colours. 
 
 65 
 
 Yellow — continued. 
 
 Ochre-yellow : 
 
 ochre. 
 
 Wine-yellow : 
 
 fluor. 
 
 Cream-yellow : 
 
 halloysite. 
 
 Orange-yellow : 
 
 vndfenite. 
 
 
 Bed. 
 
 Aurora-red : 
 
 realgar. 
 
 Hyacinth-red : 
 
 essonite. 
 
 Brick-red : 
 
 polyhalite. 
 
 Scarlet-red : 
 
 cinnabar (earthy). 
 
 Blood-red : 
 
 pyrojpe. 
 
 Flesh-red : 
 
 heiilandite. 
 
 Carmine-red : 
 
 chalcotriehite. 
 
 Cochineal-red : 
 
 cinnabar (crystallised). 
 
 Kose-red : 
 
 rose-quartz. 
 
 Crimson-red : 
 
 ruhy. 
 
 Peachblossom-red : 
 
 lepidolite. 
 
 Colnmbine-red : 
 
 almancUne. 
 
 Cherry-red : 
 
 Jcermesite. 
 
 Brownish-red : 
 
 jasper. 
 
 
 Beown. 
 
 Eeddish-brown : 
 
 tile ore. 
 
 Clove-brown : 
 
 axinite (massive). 
 
 Hair-brown : 
 
 harytes (stalaeiitic). 
 
 Chestnut-brown : 
 
 jasper (Egyptian). 
 
 Yellowish-brown : 
 
 p'zibramite. 
 
 Wood-brown : 
 
 asbestos (mountain wood). 
 
 Liver-brown : 
 
 menilite. 
 
 Blackish-brown : 
 
 limonite. 
 
 Window- 
 case III, 
 
 A suite of colours of a single mineral -.—fluor. 
 
 Play of colours : — precious opal. 
 
 Change of colours : — lubradorite. 
 
 Tarnish : — tetrahedrite. 
 
 Iridescence -.—quartz. 
 
 Opalescence : — moonstone. 
 
 Asterism : — star-stone. 
 
 Pleochroism : — dichroite. 
 
66 Other optical characters. 
 
 Fluorescence : — amber. Window- 
 
 _, , ^ case III. 
 
 Phosphorescence :^fmor. 
 Refraction and Polarisation : — 
 
 Single refraction : salt. 
 
 Double refraction (and plane polarisation) : calcite. 
 
 Circular polarisation : rock-crystal. 
 
 The Degrees of Transparency : — 
 
 Transparent : rocJe crystal. 
 
 Semi-transparent : - calcite. 
 
 Translucent : milky quartz {massive). 
 
 Semi- or sub-transiucent : hornstone. 
 
 Opaque : eisenkiesel. 
 
 Lustre : — 
 
 The kinds of lustbe — 
 
 Perfect metallic : pyrites. 
 
 Imperfect (or sub-) metallic : pitchblende. 
 
 Common adamantine : blende (transparent). 
 
 Metallic adamantine : blende (black), 
 
 ' Resinous : eolophonite. 
 
 Vitreous : celestine. 
 
 Waxy : wax-opal. 
 
 Common pearly : heulamdite. 
 
 Metallic pearly : hronzite. 
 
 Silky : crocidolite. 
 
 The degeees of intensity of lustbe — ■ 
 Splendent : blende. 
 
 Shining : calcite. 
 
 Glistening : tnagnetite. 
 
 Glimmering : galena, 
 
 Dull : haolinite. 
 
 Streak : — 
 
 Shining : argentite. 
 
 Of the same colour as the mineral : calcite, malachite. 
 Of a different colour from the mineral : crocoisite, hsematite, 
 limonite, copper-pyrites. 
 
structure. 
 
 67 
 
 The specimens in window-case IV. relate to the remaining Window- 
 characters of minerals. **** ^^• 
 
 Cleavage : — 
 Tede cleavage — Salt, galena, jluor, blende, apophyllite, 
 cahite, corundum, mica, stibnite, topaz, harrjtes, selenite, 
 hornblende, microcline. 
 
 Faces of union — sahlite. 
 
 Fracture : — 
 Conchoidal : 
 Sub-conchoidal : 
 Uneven : 
 Even : 
 Splintery : 
 Hackly : 
 
 Structure : — 
 Cbystalline — 
 
 Laminae — 
 Flat: 
 
 Flat and divergent : 
 Curved : 
 
 caldte, fiint, laryfes. 
 quartz, 
 semiopal. 
 limestone. 
 Jade, 
 copper. 
 
 marble, coccolite, 
 
 slate spar, 
 pyrophyllite. 
 specular iron. 
 
 FiBEOXJS TO Columnar — 
 Straight : asbestos. 
 
 Curved : bosjesmanite. 
 
 Straight and parallel : gypsum, tremolite, satin-spar. 
 Kadiating : wavellite, natrolite. 
 
 Divergent : celestine. 
 
 Matted : pilolite. 
 
 Columnar : anthraconite. 
 
 Geanulab — 
 Coarsely : 
 Finely : 
 
 magnetite, colophonite, 
 magnetite. 
 
 Complicated — 
 
 Layers : agate, onyx, calcite, pisolite. 
 
 Curved layers made up of grains : allemontite. 
 Curved layers made up of fibres : hasmatite. 
 
 E 2 
 
68 Hardness and specific gravity. 
 
 Sectility: — chlorargyrite. Window- 
 
 Malleability : — argentite. 
 Ductility : — copper. 
 Prangibility : — 
 
 Brittle : sulphw. 
 
 Tough : jibrolite. 
 
 Soft : malyhdenite. 
 
 Friable: sassoline. 
 Flexibility : — talc. 
 Elasticity : — mica. 
 Hardness : — 
 
 The scale of hardness. 
 
 1. Tale. 6. Adularia. 
 
 2. BoeJc-salt. 7. Quartz. 
 8. Calcite. 8. Topaz. 
 
 4. Fluor. 9. Gorv/ndAMi. 
 
 5. Apatite. 10.- Diamond. 
 
 Differences of hardness on different faces of the same 
 
 crystal : calcite. 
 Differences of hardness along different directions in the 
 
 same face : salt. 
 
 case IT. 
 
 Specific gravity (relative to that of water) : — 
 Between 1 and 2 : mellite. 
 
 „ 2 and 3 : 
 
 3 and 4: 
 
 „ 4 and 5 : 
 
 quartz. 
 
 topaz. 
 
 zircon. 
 
 
 5 and 6 : 
 
 hournonite. 
 
 6 and 7: 
 
 scheelite. 
 
 
 7 and 8 : 
 
 wolfram. 
 
 
 „ 8 and 9 : 
 9 and 10 : 
 
 copper, 
 bismuth. 
 
 
 „ 10 and 19 : silver, amalgam, gold, platinum. 
 Magnetic characters : — 
 Pabamagnetio — 
 
 Strong, with polarity : 
 Strong, without polarity : 
 Weak: 
 
 magnetite, 
 magnetite, 
 ilmenite. 
 
 DiAMAGNETIO— 
 
 
 bismuth. 
 
other characters. 
 
 69 
 
 Electrical characters : — 
 
 Due to pressure : calcite. 
 
 Due to friction : amher, topaz. 
 
 Due to changing temperature (pyro-electricity) : tourma- 
 line, horacite. 
 
 Due to difference of temperature at the points of contact 
 with another substance (thermo-electricity) : bismuth, 
 pyrites. 
 
 case IV, 
 
 Conductivity — 
 Good : silver. 
 Bad : diamond. 
 
 Thermal characters : — 
 
 Dilatation : calcite. 
 
 Action upon radiant heat : rock-salt. 
 
 Conductivity : quartz. 
 
 Touch : — 
 
 
 Unctuous : 
 
 steatite.' 
 
 Meagre : 
 
 tripoli. 
 
 Harsh : 
 
 trachyte. 
 
 Adhesive to the tongue : 
 
 hydrophan'e. 
 
 Smell :— 
 
 
 Bituminous : 
 
 elaterite. 
 
 Sulphurous (on friction) : 
 
 pyrites. 
 
 Garlic-like (on friction) : 
 
 mispickel. 
 
 Empyreumatic (on friction) : 
 
 anthraconite. 
 
 Clayey (on breathing) : 
 
 Jcaolinite. 
 
 Taste : — 
 
 
 Astringent : 
 
 chalcanthite. 
 
 Sweetish astringent : 
 
 alum. 
 
 Saline : 
 
 salt. 
 
 Alkaline : 
 
 natron. 
 
 Cooling : 
 
 nitratine. 
 
 Bitter : 
 
 epsomdte. 
 
( 70 ) 
 
 EECENT ADDITIONS. 
 
 For a short time previous to their dispersion througk the Window- 
 General Collection, recent additions are arranged for inspection '^^^ ■ 
 in the fifth window-case on the left-hand sid« of the Gallery, 
 
 In the remaining fifteen window-cases of the Gallery are 
 arranged series intended rather for those who are making a 
 minute study of minerals, and are provided with text-books, 
 than for the readers of a Guide, 
 
 THE CRYSTALS AND CRYSTAL MODELS. 
 
 In window-cases VI.-IX. is a series of specimens illustrative wiudow- 
 of the manifold character of crystalline form. In addition to ^jj ^'■' 
 specimens of crystals met with in Nature, there is displayed a fine 
 suite of so-called artificial crystals prepared by Carl von Hauer, 
 and presented to the Trustees in 1862 by Her Majesty the 
 Queen, The term a/rtificial is in such case intended to imply, 
 not that the specimens have been cut, but merely that the 
 conditions under which the crystals have been deposited from 
 solution have been artificially induced. 
 
 Those at the end of window-case IX, are instructive as 
 examples of the character of isomorphism ; in each instance a 
 crystal of one kind of substance has been transferred from the 
 solution in which it has been formed to another which would 
 deposit crystals of the same shape ; instead of being destroyed, 
 as is generally the case when a soluble crystal is immersed in a 
 diflerent kind of solution, the specimen has continued to grow. 
 In some of the examples the change has been repeated several 
 times, as is particularly evident where the solutions have been 
 of different colours. 
 
 Window-cases X,-XIII, contain a series of crystal'models 
 invaluable to the student. 
 
( 71 ) 
 
 THE PSEUDOMORPHS. 
 
 In the remaining window-cases, XIV.-XX., is shown a most 
 extensive and instructive series of pseudomorphs — that is to say, 
 minerals presenting a form characteristic, not of their own, but 
 of some other substance. Pseudomorphs illustrate the decom- 
 posing influences to which many minerals have been subjected, 
 and they throw valuable light on the order of succession in 
 which, and the conditions under which, particular minerals 
 have been formed and deposited ; and, in furnishing us with 
 sure proofs of conversions which we can never hope to effect 
 in the laboratory, they afford us a knowledge of facts which 
 can be arrived at in no other way. 
 
 Pseudomorphs are of three kinds, due respectively to Encrus- 
 tation, Alteration, and Eeplacement of the original mineral. 
 By encrus- In window-case XIV. are shown the Encrustation pseudo- 
 tation. morphs, or epimorphs, as they are sometimes called ; in these 
 
 the pseudomorphous mineral obtains its form through simple Window- 
 encrustation of crystals of another mineral. As a good example "^^^^ ^^^'• 
 may be mentioned the first specimen in the case, where thin 
 crusts of quartz have the form of crystals of calcite. 
 B7 altera- In window-cases XV., XVI. and XVII., are the Alteration 
 tion. pseudomorphs, arranged in groups according to the kind of 
 alteration which has taken place : 
 (i.) Loss of a constituent ; or, 
 
 (ii.) Grain of a constituent, both in window-case XV. ; or, 
 
 (iii.) Exchange of constituents, in window-cases XVI. and 
 XVII. 
 
 An example of the first group is the first specimen in Window- 
 window-case XV., in which cuprite, a compound of copper and '^*^'' ^^' 
 oxygen, has lost its oxygen and been altered to copper. 
 
 As an example of the second group we may indicate the first 
 specimen beneath the middle pane of the same case, in which 
 cuprite has been altered to malachite through the addition of 
 carbonic acid and water. 
 
72 Pseudomorphs. 
 
 An example of the third group is furnished by the first Window- 
 specimen in window-case XVI., in which pyromorphite, ^''^^^ x^l^ 
 compound of phosphate and chloride of lead, has been altered 
 to galena, a sijlphide of lead, through the replacement of 
 the arsenic acid and the chlorine by sulphur. 
 
 In each of these specimens the form of the original mineral 
 has been retained. 
 By replace- In window-cases XVIII. and XIX, are the Eeplacement window- 
 "^°'* pseudomorphs, in which there has been a complete substitution ^^j ^nd 
 of one substance for another. A good example of this kind of xix. 
 pseudomorph is the first specimen in window-case XVIII., where 
 haematite (oxide of iron) has the form of calcite (carbonate of 
 lime). 
 Para- The first specimens in window-case XX. are of the kind Window- 
 '""'■p s- ]jQo^jj as paramorphs, in which there has been a re-arrange- "**" 
 ment of the molecules and a corresponding alteration in the 
 mineral characters, the percentage chemical composition and the 
 form, however, remaining imchanged. 
 Psendo- These are followed by some minerals which have the forms 
 morphs ^f various organic remains; they afford a very convincing 
 organic proof of the possibility of a change of substance without 
 remains, alteration of form. 
 
 The Finite As a Supplement to the collection of pseudomorphs, there is 
 group. ^igQ arranged in this case, a series of minerals known as the 
 Finite group. Most of them result from the alteration of 
 dichroite, and their composition, depending as it does on the 
 extent of the alteration, is too indefinite to allow of the 
 products being classed with the simple minerals. 
 
( 73 ) 
 
 THE MINERAL SPECIES AND 
 THEIR VARIETIES. 
 
 DIVISION I. 
 
 THE NATIVE ELEMENTS. 
 
 Of the 65 elementary bodies into which matter lias been 
 resolved by the chemist, the few which have been found in 
 Nature in the uncombined state are shown in cases 1 and 2 : 
 they are arranged in two sections, Metallic and Non-Metallic 
 elements. This division of the elements, though convenient, is 
 quite arbitrary, for no sharp line of division can be drawn 
 between the two sections. 
 
 Section!.— With the native metals are placed the native alloys, or 
 Metals, compounds and mixtures of metals which belong to the same 
 chemical group. 
 
 Copper. This native metal, with silver and gold, has been 
 known from the earliest times. The first locality known to the ^*^° ^^^'' 
 ancients is said to have been the Island of Cyprus, and to 
 the name of that island the word copper is itseK related. The 
 toughness of the metal, and the hardness of its alloys made 
 it highly valued by the ancients as a material for tools and 
 weapons. 
 
 During the present century the finest crystals and the largest 
 masses have been furnished by the mines of Eussia and of 
 the neighbourhood of Lake Superior : in one of the mines of 
 the latter locality there was found, in 1859, a mass estimated 
 to weigh upwards of 400 tons ; its length was 45 feet, and its 
 greatest width and thickness 22 feet and 8 feet, respectively ; 
 40 men were employed for 12 months in extracting it. 
 
74 Native metals.. 
 
 Though the crystals of native copper are rarely symmetrical 
 in appearance attention may be directed to the branch of cubes 
 from the Lake Superior mining region, (case lb) and to the 
 groups and tree-like growths of crystals from the mines of the 
 Urals (case la). As instances of the variety of form of the 
 native metal we may also mention ; — the large irregular water- Case la. 
 worn mass brought from a copper mine near the Copper- 
 mine Eiver by Mr. Hearne and presented to the Trustees in 
 1818 ; the thin plate from Barr Head, Eenfrew ; the dendritic Case lb. 
 and the mossy growths from Cornwall ; and the long branches 
 from the Lake Superior district, of which the largest (presented 
 by Prof. Euskin) is to be seen in the lower part of the case. 
 
 Silver is found native in a large variety of forms and in Cases 
 many localities. "^ "" 
 
 Magnificent specimens have been obtained from the mines 
 of Kongsberg in Norway: one of them, now in the Eoyal 
 Collection at Copenhagen, weighs upwards of 5 cwt. 
 
 Amongst the specimens here shown we may remark: — 
 dendritic growths from Potosi, Freiberg and Peru ; bundles of 
 coarse fibres from Chaiiarcillo ; groups of fine curved fibres 
 from Wheal Vincent, Cornwall ; and native foil from Sultepec 
 mine, Mexico ; all in case Ic : a nugget, weighing thirty-seven 
 ounces, from Peru; a mass of crystals and a long branch 
 from Kongsberg ; all in case 2a. 
 
 Native silver is seen intermingled with native copper in the C*^« i"- 
 specimens from Lake Superior : when fused together and 
 allowed to cool under ordinary circumstances, an alloy of the 
 two metals is formed. 
 
 GrOLD, one of the most widely occurring of minerals, is almost Case 2b-e. 
 always found either in and about veins of quartz-rock or in 
 alluvial deposits. 
 
 The native gold from our own islands, in case 2b, and the 
 various nuggets from Australia and California brought together 
 in case 2d, are well worthy of attention ; the Latrobe nugget 
 is especially remarkable as showing crystalline structure, A 
 fine suite of specimens, collected in Brazil by Captain Lyon, Case 2d. 
 E.N., is exhibited. 
 
 Specimens illustrating the varieties of crystalline form will 
 be found in case 2c. Other forms of occurrence are the leaf- 
 
Native metals. 75 
 
 gold and the deiidritic growths, of which many specimens are 
 shown in case 2c and 2e. 
 
 A large mass of quartz from Costa Rica, estimated to con- 
 tain above 50 oz. of finely divided gold, will be seen in the 
 lower part of case 2. 
 
 The rare association of visible gold with galena is illustrated 
 by specimens from Beresovsk and the Argentine Confederation 
 (case 2b); while specimens from Adelfors (case 2b) and the 
 Solferino reef (case 2d), show the exceptional occurrence of 
 gold in carbonate of lime. 
 
 Native gold always contains more or less silver, and when 
 the proportion reaches about 20 per cent, is called Eleetrwn ; the Case 2e. 
 crystalline forms of electrum are generally much more sharply 
 defined than are those of the purer gold. Beautiful specimens 
 of the pale gold from Transylvania are shown in case 2e ; the 
 percentage of silver in some of the specimens from that country 
 reaches 38 per cent. 
 
 A variety of gold called Porpezite is rich in palladium ; a 
 small specimen is shown in case 2c. 
 
 Models of some of the most interesting gold nuggets are 
 shown in the upper and lower parts of the case. 
 
 Iron, Lead and Tin are of very restricted occurrence in the Case 2ef. 
 native state ; almost all the iron thus met with is believed to 
 have fallen from the sky, and many specimens of it are shown 
 in the Collection of Meteorites in the Pavilion : the iron found 
 at Ovifak by Professor Nordenskiold is, however, now regarded 
 by most mineralogists as having had a terrestrial origin. The 
 iron of commerce is obtained from its " ores," among which we 
 may especially mention magnetite, haematite, limonite, chalybite 
 and clay iron-stone: the lead of commerce is in great part 
 extracted from galena, a compound of lead with sulphur ; and 
 the tin of commerce from cassiterite or tin-stone, a compound 
 of tin with oxygen. 
 
 Platinum is another valuable native metal, generally foimd Case 2f. 
 in small grains but occasionally in rather large nuggets ; one 
 in the case weighs upwards of forty ounces. The metal was 
 first met with in South America. After its discovery in the 
 Urals an attempt was made to introduce a platinum coinage in 
 Eussia, but without success, owing to the irregularity iu the 
 
76 Native, metals. 
 
 amount produced, though platimim to the value of £400,000 is 
 said to have been coined between 1826 and 1844. Platinum is 
 one of the heaviest metals known: it weighs in the native 
 state 17 or 18 times, and when purified 21J times, as much 
 as an equal volume of water. It is almost infusible, and is 
 attacked by few substances, properties which render it of great 
 value as a material for chemical apparatus. 
 
 Ieidosmine is a rare mineral containing the metals iridium Case 2f. 
 and osmium, and is generally found associated with platinum. 
 It is used for the tips of the nibs of gold pens, on account of 
 its hardness and the difficulty with which it is acted upon 
 by acids. 
 
 Mebouey, or Quicksilver, though found native, chiefly as Case 2f. 
 small globules, is generally extracted from the mineral cinna- 
 bar, in which it exists in combination with sulphur. Though 
 metallic in its general characters it is remarkable as being 
 liquid at ordinary temperatures; it is the densest liquid 
 known, being 13J times as heavy as its own volume of water. 
 It is much used for thermometers and barometers, the silvering 
 of mirrors, the extraction of gold and silver from their ores, and 
 the preparation of the artificial compound with sulphur, the 
 vermilion of commerce. 
 
 Native Amalgam. The " mixtures " of mercury with other Case 2f. 
 metals are called amalgams. That known as native amalgam 
 is found almost wholly in the Landsberg mine in the canton of 
 Ober-Moschel, Ehenish Bavaria ; it contains from 25 to 35 per 
 cent, of silver. Remarkably good crystals are shown in the case. 
 
 Arsenic, antimony and bismuth form a group of metals of 
 ■which the crystals present the symmetry of the Khombo- 
 hedral system and have almost identical angles : with these 
 is placed the much rarer element tellurium, of -which the Case 2h. 
 crystals present similar characters ; its chemical properties, 
 however, associate it rather with the element sulphur, which 
 immediately follows it in the arrangement of the Collection. 
 
 Arsenic is rarely found in distinct crystals : it is often 
 granular in structure and mammillaiy in shape : though initially Ca8e-2g. 
 tin-white it is soon altered to a dark grey by exposure. Simple 
 metallic arsenic is not itself of much importance in the arts, but 
 the alloy with lead has been found useful as a material for the 
 
Non-metallic elements. 77 
 
 manufacture of shot. The metallic arsenic required for com- 
 merce is for the most part obtained by roasting mispickel, a 
 compound of arsenic with sulphur and iron. 
 
 Antimony, though found native, is chiefly obtained for ^^^^ H- 
 commerce from the much more plentiful mineral stibnite, in 
 which the metal is combined with sulphur. It is very 
 valuable for the manufacture of type-metal, an alloy of 
 antimony with lead and tin : this alloy, like water, presents 
 the exceptional property of increasing in volume when passing 
 from the liquid to the solid state ; it thus, whilst solidifying, 
 keeps in constant contact with the mould and takes a sharp 
 impression. Britannia metal and pewter are alloys of antimony 
 with tin. 
 
 Allemontite is remarkable as being a compound of the two Case 2g. 
 similar elements antimony and arsenic : of the latter it 
 contains 65 per cent. 
 
 Bismuth is chiefly found native : a very fine mass from Bolivia, Case 2g. 
 rich in gold, is shown in the lower part of the case : specimens 
 also are shown from Cornwall and Saxony, This metal has the 
 peculiar property of forming alloys with lead and tin which melt 
 at a very low temperature, some of them far below the boiling 
 point of water : these alloys are much used in the process of 
 stereotyping. The metal is also employed in the manufacture 
 of some kinds of solder. 
 
 Section ii. In the second section of native elements is placed sulphur ; 
 ~ and also diamond and graphite, the two native modifications 
 metallic of the element carbon, 
 elements. gtJLPHUR. The Specimens of this mineral are from their Cases 
 
 colour, transparency, size, and sharpness of crystalline form, 
 among the most magnificent of natui-al products : very fine 
 groups of crystals from Sicily and Spain will be found in the 
 upper and lower parts of the case. Sulphur generally occurs 
 in the neighbourhood of volcanoes, active or extinct, and is 
 often associated with gypsum. Most of the sulphur required 
 for commerce is brought in the native state from Sicily : in 
 France, Germany and Sweden it is also artificially prepared by 
 
 2h, lef. 
 
78 Non-metallic elements. 
 
 distillation from pyrites. It is employed in medicine (the 
 common brimstone) ; and also in the manufacture of gun- 
 powder and of oil of vitriol. 
 
 Diamond and Geaphite, though chemically only different Case if-h. 
 states of the element carbon, are almost completely opposite in 
 their general characters. The diamond is the hardest of all 
 known minerals ; graphite is one of the softest : diamond is 
 generally found in very symmetrical transparent crystals, 
 generally colourless or faintly yellow, but sometimes with 
 blue, grey, or other tints ; graphite, on the other hand, rarely, 
 if ever, occurs in weU defined crystals ; it is opaque, black in 
 colour, and has a metallic lustre quite different from that of 
 the diamond: diamond, too, is a very bad conductor of elec- 
 tricity, graphite an excellent one. 
 
 The diamond, from its rarity and hardness, has long been 
 regarded as the most precious of the decorative stones ; its 
 superiority of lustre and brilliancy have been rendered even 
 more conspicuous by the discovery, made not many centuries 
 ago, that this, the hardest of stones, can be cut and polished 
 by means of its own powder. 
 
 The diamond becomes strongly electric on being rubbed : 
 when it is heated or exposed to a strong light it becomes 
 luminous, and retains the character for several hours. 
 
 The collection of mounted crystals is extremely remarkable Case ig. 
 as representing a great variety of crystalline form. A very 
 symmetrical South African crystal, weighing 130 carats, the Case if. 
 property of Professor Euskin, is exhibited; the triangular 
 markings on the octahedral faces, so characteristic of the dia- 
 mond, are in this specimen extremely distinct. 
 
 Models of some of the most famous diamonds are shown in 
 the case. 
 
 Those specimens which are useless to the jeweller, owing to 
 imperfect crystallisation (when the specimens are known as Case if. 
 Boa/rt) or to flaws, have considerable value for the lapidary, by 
 whom they are reduced to powder and employed in cutting and 
 polishing the precious stones. 
 
 There is found in Brazil a black uncrystallised variety of 
 carbon, called Carbonado, which has the hardness of the dia- Case if. 
 mond, and is in much request for the drilling of hard rocks : 
 
Non-metallic elements. 79 
 
 to this purpose the diamond itself is not suited, for, notwith- 
 standing its great hardness, it easily splits in certain direc- 
 tions related as usual to the crystalline form ; of this property 
 the diamond-splitter avails himself for removing the parts con- 
 taining flaws, and for shaping the specimens before the polish- 
 ing is begun. Very few diamonds are now found in India, 
 where the once famous mines of Golconda are situated : almost 
 all those of commerce are brought from Brazil and South 
 Africa. 
 
 It is not known how the diamond has been produced in 
 Nature, and it is even doubtful whether it has ever been found 
 in the place where it was originally formed : specimens of the 
 pebbles amongst which the diamond has been met with in 
 Brazil and India and of the rocks in which it occurs in South 
 Africa, are shown in the case. 
 
 Gkaphite, also known as TlvmJ>ago or BlaeMead, has many Case ih. 
 uses. In its purest form it is the material of blacklead 
 pencils : excellent graphite for this purpose was long supplied 
 by the mines of Borrowdale in Cumberland, now worked out. 
 The less pure forms are employed for the polishing of stoves 
 and for reducing the friction of machinery ; large quantities 
 from Ceylon are mixed with clay and made into crucibles at 
 the Battersea works. 
 
 The specimens from New Cumnock show a columnar 
 structure, probably caused by the heat from a neighbouring 
 trap-dyke. A curious fibrous structure is also conspicuous in 
 some of the specimens from Battugol. 
 
 DIVISION 11. 
 
 THE COMPOUNDS OF METALS WITH ELEMENTS 
 OP THE ARSENIC AND SULPHUR GROUPS. 
 
 In the first of the four sections of this division are placed 
 those minerals in which arsenic, antimony or bismuth is 
 combined with a metal of another group : the second section 
 includes those compounds of metals with sulphur, selenium 
 or tellurium, in which the latter are regarded as playing a 
 
80 
 
 Arsenide group. 
 
 Section i. — 
 
 the 
 
 arsenide 
 
 group. 
 
 part analogous to that of oxygen in the oxides : in the third 
 section are arranged the minerals wherein certain arsenides 
 of section i. are combined with the sulphides of section ii., 
 or which may otherwise he looked upon as the result of 
 a replacement of half the arsenic of the minerals of section i. 
 hy its equivalent of sulphur : the fourth and last section 
 comprises those minerals in the chemical constitution of 
 which sulphur is regarded as playing a part analogous to 
 that of oxygen in the oxygen-salts, a class of compounds ' 
 hence termed sulphur-salts. 
 
 Dysceasite is a compound of antimony and silver, and Case 3a. 
 contains from 77 to 85 per cent, of the precious metal. 
 
 NiCKELiNE is a compound of nickel and arsenic, and an Case 3a, 
 important source of the nickel of commerce ; the alloy of this 
 metal with copper and zinc is the well-known German silver. 
 The metal is at present chiefly used for electroplating with 
 silver. 
 
 Smaltine, a compound of cobalt and arsenic, is the mineral Case 3b. 
 from which blue enamel colours, particularly smalt, are 
 prepared. 
 
 Chloanthite is the corresponding compound of nickel and Case 3c, 
 arsenic, and is another source of the metal nickel. 
 
 Skutteeudite is a compound of cobalt and arsenic, crystal- Case 3c, 
 lising in forms analogous to those of pyrites. 
 
 Section ii, 
 —the 
 sulphide 
 group. 
 The mono- 
 sulphide 
 series. 
 
 Akgentite is an important ore of silver, 100 parts contain- Case83d,4a. 
 ing 87 of that metal combined with 13 of sulphur: before 
 exposure to the light it has a bright metallic lustre, but soon 
 after exposure becomes coated with a dull dark powder : the 
 mineral is remarkable as being perfectly sectile. Good 
 specimens from Freiberg, Chili, and also Cornwall, will be 
 found in the cases. 
 
 Blende is an important ore of zinc : 100 parts of the case 4b-d, 
 mineral contain 67 of zinc and 33 of sulphur. 
 
 A particularly fine suite of specimens is shown in the case. 
 Specimens of blende containing the new and rare element Case 4d. 
 gallium, presented by Mr. W. G. Lettsom, are exhibited. 
 
 Occurring in many parts of the world and having been 
 produced under many different conditions, the crystals of 
 
Monosulphide series. 81 
 
 Hende present a considerable variety in their forms, 
 all of which can be referred to that section of the Cubic 
 system of which the tetrahedron is a prominent type, and 
 they thus afford material for the study of that kind of 
 hemihedry. It has been found that while all alternate faces 
 of the octahedron are similar to each other, the adjacent 
 ones differ in lustre, striation and smoothness, and also in 
 the angles which the associated faces make with them. The 
 crystals are rarely simple growths, being generally twinned 
 upon the faces of the octahedron. 
 
 GrALENA is by far the most important ore of lead : 100 parts Case 4e-h. 
 of the mineral contain 87 of lead and 13 of sulphur. The 
 crystals from Rossie and fromNeudorf are very sharply defined. 
 A large crystallised specimen from the Great Laxey mine is 
 shown in a corner of the Pavilion, 
 
 Alabandite is the corresponding compound of manganese and Case 4h. 
 
 sulphur. 
 Pentlandite is a compound of iron, nickel and sulphur, Case 4h. 
 
 and is commercially important as a source of nickel. 
 
 Copper-glance, or Eedruthite, is an important ore of Case 3e-g. 
 copper: 100 parts contain 80 of copper and 20 of sulphur. 
 The suite of specimens from Cornwall is unique for excellence 
 and variety of crystalline form. The mineral is altered by 
 exposure to light. 
 
 - Cinnabar is the ore from which mercury (or quicksilver) is Cases 
 obtained by heating : 100 parts contain 87 of mercury and 13 ^^' ^''■ 
 of sulphur : the same compound artificially prepared is the 
 vermilion of commerce. Almost the only localities known are 
 those of Almaden in Spain, Idria in Austria, Moschel in 
 Rhenish Bavaria, and New Almaden in California. 
 
 WuRTZiTE is interesting as crystallising in the Ehombohedral Case 5a. 
 system, though it has the same chemical composition as 
 blende. 
 
 Greenockite is a very rare mineral found in association with Case 5ab. 
 prehnite and stilbite ; it was first met with in cutting 
 the Bishopton tunnel on the Glasgow and Greenock 
 railway ; it is a compound of sulphur and cadmium. The 
 corresponding artificial compound is the pigment cadmium 
 yellmo. 
 
 MiLLEKlTE is another source of the metal nickel : the wool- Case 8b. 
 like form from St. Louis is worthy of notice. Considerable 
 
 F 
 
82 Disulphide series. 
 
 quantities of this mineral have been obtained from the Gap 
 mine, Lancaster county, Pennsylvania. 
 
 Ceookesite, is remarkable as containing 17 per cent, of Case 5c. 
 
 thallium : it is a selenide of copper and thallium with about 
 
 5 per cent, of silver. 
 NagyIgite is a telluride of gold and lead, in which some of Case 5c. 
 
 the tellurium is replaced by sulphur. 
 
 senes. 
 
 The Hatjerite, beginning the series of disulphides, is the Case 5d. 
 
 disulphide disulphide of manganese ; its crystals present the same 
 
 kind of hemi-symmetry as those of pyrites. 
 
 Pyeites, or Iron-pyrites, contains 47 of iron and 53 of sulphur Cases 
 in 100 parts. Though one of the most common of minerals, the ^'*' ®*''- 
 difficulty of getting rid entirely of the sulphur prevents it from 
 being employed for the manufacture of iron : it is, however, 
 extensively used in the preparation of the green vitriol and oil 
 of vitriol of commerce. 
 
 Just as blende is useful for the study of that hemi-symmetry 
 of the Cubic system in which only the symmetral character 
 of the cube-planes is in abeyance, so pyrites with its mani- 
 fold forms is of the greatest value for the study of that 
 kind of hemi-symmetry in which only the symmetry relative 
 to the dodecahedron-planes is wanting. The specimens from 
 Elba and Traversella are especially worthy of remark. 
 
 Gr. Eose with very doubtful success has sought to prove that 
 the complementary semiforms of this mineral are associated 
 with opposite thermo-electric characters. 
 
 Makcasite, having the same chemical composition and the case 6b. 
 same commercial uses as the last named mineral, has from its 
 lighter colour beeh called " White iron pyrites ; " but the 
 differences in the crystalline form and other characters make it 
 necessary to regard the two kinds as different species. The 
 crystals of marcasite are far from being so distinctly formed as 
 those of pyrites. They generally group themselves into peculiar 
 shapes, thus giving rise to the fanciful terms, Spear pyrites. 
 Cockscomb pyrites, &c. 
 
 Molybdenite is the disulphide of . molybdenum, and is the Case 6c. 
 chief source of the molybdenum salts ; it is very similar in 
 
A rseno-sulphide group. 83 
 
 appearance to graphite, from wHch it was only distinguished 
 in 1778. 
 Realgar is the disulphide of arsenic, and occurs in crystals Case 60. 
 of a beautiful aurora-red colour ; as on exposure to light the 
 mineral is soon altered to a yellow powder, the specimens are 
 kept in the drawers. 
 
 The sesqui- Laueite is a Sulphide of the rare element ruthenium, of which Case 6d. 
 
 Series metal part is replaced by osmium : it has only been found 
 
 in Borneo, where it occurs associated with platinum. 
 Stlvanite is a telluride of silver and gold. Case 6d. 
 
 Stibnite, or Antimonite, a compound of sulphur and antimony, Case 6e. 
 is much used for the preparation of the metal and its salts, of 
 which a large number have been employed in medicine : in the 
 East the powdered mineral is used for painting the eyebrows. 
 The specimens from Felsobanya ajid* Japan are especially 
 worthy of notice ; a magnificent specimen from the latter locality 
 is shown in the Pavilion., 
 
 BiSMTiTHiTE is the corresponding sulphide of bismuth. Case 6f. 
 
 Obpiment is the corresponding compound of sulphur and Case 6g. 
 arsenic : the artificial compound was one of the ingredients of 
 the pigment "kings yellow, now superseded by the harmless 
 chrome-yellow. 
 
 Section iii. CoBALT-GLANOE, or Cobaltine, like smaltine, is highly valued Case 6g. 
 ~^^^ as an ore of cobalt : and is a compound of that metal with 
 
 arseno- . , _ ^ '■ .., 
 
 sulphide arsenic and sulphur, its crystals are similar to those of 
 group, pyrites in the development of their faces, 
 
 NiCKEL-GLAifCE is the corresponding compound of nickel ; and Case 6g. 
 TJllmannite is a similar compound of nickel, in which 
 the greater part of the arsenic is replaced by antimony. 
 
 M18PICKEL, a compound of arsenic, sulphur and irouj is the Case 6h. 
 chief source of the arsenical compounds of commerce, 
 
 Danaite is a variety of mispickel containing cobalt. Case 6h. 
 
 Glaucodote is a similar compound, in* which still more of the Case 6h. 
 iron has given place to cobalt. 
 
84 Sulphur-salts. 
 
 Section iv. The first and somewhat ambiguous group of sulphur-salts 
 
 —the is regarded as containing FejSg or FeSj as part of the 
 
 sulphur- "acid" component. 
 
 ■salta. Pykehotine, or Magnetic pyrites, is a compound of iron Case 5e. 
 
 and sulphur. The specimen from Morro Velho, presented 
 in 1883 by Mr. Y. Tendron, is unusually fine ; good speci- 
 mens are also shown from the Miggiandone mine. 
 
 Erubescite is a valuable ore of copper, and contains that Case Se. 
 metal in combination with sulphnr and iron ; the copper varies 
 from 60 to 70 per cent. 
 
 CopPEK-PYBiTES, or Ohalcopyrlte, is the most important of Case 5f -h. 
 copper ores, and contains the same elements as erubescite but in 
 different proportions, the copper amounting to only 35 per cent. 
 It is also used for the preparation of the " blue copper " (copper 
 sulphate) of commerce. For general excellence the series of 
 specimens in the case is unequalled. 
 
 The crystals of this mineral belong to the Tetragonal system, 
 and are of great interest to the student as being almost 
 the only representatives in that system of a hemi-symmetry 
 corresponding to that of blende in the Cubic The twin- 
 growths, too, are especially important in their characters : 
 remarkably good examples of a kind of growth almost, if 
 not quite, peculiar to this mineral are shown from Cornwall 
 and Freiberg (case 5g). 
 
 The next and largest group of sulphur-salts is that consisting 
 of sulph-arsenites, sulpho-bismuthites and sulph-antimonites. 
 
 Stephanite is a sulph-antimonite of silver, and is an important Case 5h. 
 silver ore. 
 
 Teteahedeite, or Grey copper ore, a most valuable ore of copper, Case Tab. 
 belongs to this class ; it is a sulph-antimonite of that metal, 
 part of which is frequently more or less replaced by silver, 
 iron and zinc. The specimens from Cornwall, which are 
 coated with copper-pyrites and tarnished, are very beautiful. 
 
 Tennan riTE is the corresponding compound in which the Case 7b. 
 ■antimony is replaced by arsenic. 
 
 Both the latter minerals crystallise in the Cubic system, 
 • and present a hemi-symmetry similar to that of blende. 
 
 BoTJENONiTE is a sulph-antimonite of copper and lead ; the Case 7d. 
 specimens from Herodsfoot mine are unique for size and 
 splendent lustre. 
 
 Pyeaegyeite is a sulph-antimonite, and Peoustite a sulph- Case 8a-c. 
 arsenite of silver ; before they are blackened by ex- 
 
Simple chlorides. 85 
 
 posure to light they have a beautiful blood-red colour,, 
 which becomes deeper in tint as the antimony prepon- 
 derates over the arsenic, the two species being isomorphous 
 and blending the one into the other. The pyrargyrites from 
 Mexico and the Harz are particularly fine, while the mass 
 of resplendent crystals of proustite from Chili, presented 
 by Mr. H. Ludlam, is unique ; unfortunately, for the above 
 mentioned reason, it requires to be protected from the light. 
 Pyrargyrite and proustite are important ores of silver. 
 Jrdanitb is a sulph-arsenite of lead : very good crystals fromo Case 8d. 
 the Binnenthal are shown in the case. 
 
 Xanthoconite is a sulph-arsenate of silver ; of this rare Case 8e. 
 mineral a specimen from Chili, associated with proustite, 
 is probably unique for its excellence. 
 
 DIVISION HI. 
 
 THE COMPOUNDS OP METALS WITH ELEMENTS 
 OF THE CHLORINE GROUP. 
 
 Section i.— Sylvine, of which fine specimens are exhibited, is a Case 8f. 
 
 Simple compound of the metal potassium with the element 
 
 chlorides, chlorine : it is very simitar in its characters to common salt. 
 
 Salt, or Common salt, is a compound of the metal sodium Case sf. 
 with chlorine. It occurs chiefly in beds, often of great thick- 
 ness and extent, and is present in solution in salt-lakes and 
 brine-springs. The Great Salt Lake of Utah, which has an 
 area of 2000 square miles, contains 20 per cent, by weight of 
 common salt in solution. The Dead Sea contains 20-26 per 
 cent, of solid matter, and one-third of this is common salt. 
 The waters of the ocean contain 4 per cent, of solid matter in 
 solution, and about three-fourths of this is common salt. The 
 most famous mines are those of Wielicza, in Austria, which have 
 been worked for the last 600 years ; the beds of salt are there 
 so thick that they have been excavated into houses, chapels 
 and other ornamental forms, and the mines, when illuminated, 
 are regarded as one of the sights of Europe. The salt mines of 
 Cheshire are also well-known. 
 
86 Simple chlorides, &c. 
 
 A beautiful crystallised specimen from Wielicza, presented 
 in 1862 by the Austrian Government, is in the case. 
 
 Some specimens are of a deep blue colour, which disappears Case 8g. 
 when the salt is dissolved in water. 
 
 Sal-ammoniac is the corresponding compound of ammonium Case 8g. 
 and chlorine, and is found as a sublimation product near to 
 volcanoes and ignited coal seams. That required for commerce 
 is artificially prepared : it is valuable in medicine, and is also 
 used by tinmen in soldering. 
 
 Chloeakgteite, Cerargyrite or Hornsilver, contains 75 per Case 8h. 
 cent, of silver and 25 per cent, of chlorine, and is a valuable 
 ore of the metal. Chlorargyrite is remarkable for its mallea- 
 bility and sectility ; it is blackened by exposure to the light. 
 
 Embolite contains 70 per cent, of silver, the remainder con- Case 8h. 
 sisting of variable proportions of chlorine and bromine : it is the . 
 principal silver ore furnished by the mines of Chaiiarcillo, in Chili. 
 
 Fluob is a compound of calcium with fluorine : an extensive Cases 
 suite of specimens in the cases illustrates the varieties of colour ^^" ' ®* ' 
 and crystalline form presented by this beautiful mineral. 
 Large quantities, of the violet-blue variety (Blue John) have, 
 until lately, been found in veins in the limestone of Derbyshire, 
 and more especially in the large caves in the Castleton district. 
 The Derbyshire fluor is wrought into various ornamental 
 articles : it takes a good polish,' but on account of its easy 
 cleavage is difficult to work. With the exception of the pink Case 7g. 
 variety found in Switzerland, all the finest specimens of this 
 mineral are of English origin. Fluor is also employed as a flux 
 in the reduction of various ores; and the hydrofluoric acid 
 prepared from it is used for etching glass. 
 
 Calomel is a cUoride of mercury ; the artificial salt is much Case 9b. 
 
 used in medicine. 
 Fluellitb is a very rare mineral of which minute crystals Case 9c. 
 
 were found some years ago in Cornwall. It is a hydrated 
 
 fluoride of aluminium. 
 
 Section ii. Cryolite is a double fluoride of aluminium and sodium ; it Case 9c. 
 — Com- occurs forming a large bed or vein at Arksutfiord in 
 
 cHorides Greenland. It is used for the preparation of commercial 
 
 ^.(,_ ' carbonate of soda, and also of metallic aluminium. 
 
( 87 ) 
 
 I 
 
 DIVISION IV. 
 THE'COMPOUNDS OF OXYGEN. 
 
 As the chemically energetic element, oxygen, forms a fifth 
 part of the atmosphere by which our Earth is surroundecl, 
 and is by far the most important constituent of the water 
 which is nearly everywhere present, the minerals having 
 oxygen for one of their constituent elements are, as might 
 be expected, very numerous. In fact, all the minerals which 
 by their aggregation form the roots of the crust of the Earth 
 fall under this chemical division. 
 
 Just as the compoimds with sulphur are divided into 
 sulphides and eulphur-salts, the compounds with oxygen 
 are divided into oxides and oxygen-salts; the distinction, 
 though difficult to define with logical precision, yet serves 
 one important object of a system of classification in that it 
 brings together compounds which, in their general charac- 
 ters, bear a close resemblance to each other. 
 
 Oxy- At the beginning of the first section are placed the minerals 
 
 chlorides, in which oxides or hydrates are combined with the chemical 
 
 compounds which fall under the last division. 
 Matlockite is an oxychloride of lead : very fine crystals of *"ase 9c. 
 
 this mineral will bq found in the case. 
 Mbndipite is another oxychloride of lead, containing twice Case 9c. 
 
 the proportion of lead oxide present in matlockite. 
 Atacamite is a hydrated oxychloride of copper : fine crystals Case 9d. 
 from South Australia are exhibited. 
 
 &c. 
 
 The oxides are so arranged that those containing the 
 greater proportion of oxygen follow after those that contain 
 less : commencing with the basic oxides, we thus pass 
 through certain comparatively neutral oxides, among which 
 we must look for those which possess the most equivocal 
 claim to a place in the section, and we then come to the 
 higher oxides which act the part of acids in combining with 
 bases. 
 The first series is that of the monoxides. 
 
 Monoxides. CuPRiTE, or Euby copper, is an important ore of copper, of Case lOa-c. 
 which metal it contains 89 per cent. It is foimd in beautiful 
 transparent ruby-coloured crystals, which are rapidly blackened 
 by exposure to li^ht. Cuprite gives a very intense red colour to 
 glass. 
 
88 Monoxides^ epitritoxides, 
 
 Ghalcotriehite is a variety of cuprite in which the crystals are Case lOc. 
 bright red and capillary, and are not so subject to alteration by 
 light. Unequalled specimens both of cuprite and of chalco- 
 trichite are in the collection. 
 
 Tile ore is an earthy variety of the same mineral. Case lOb. 
 
 Periclasb, the con-esponding oxide of magnesium, has been Case lOc. 
 found only in the agglomerates of Monte Somma. 
 
 ZiNciTE, or SpartaUte, is a very valuable ore of zinc found Case lOc. 
 only in New Jersey : the red colour is probably due to a 
 small proportion of an oxide of manganese. The corre- 
 sponding artificial compound is used as a white paint. 
 
 Melaconite, or Black copper, is another compound of oxygen Case lOc. 
 and copper, and contains 80 per cent, of the metal. In 
 some mines it has been found in qxiantities sufficient to 
 make it a very valuable ore. 
 
 Beucite is a hydrate of magnesium : the specimens from Case lOd. 
 Wood's mine are unusually fine. 
 
 Epitrit- The next series in the section of oxides is formed by 
 
 oxides. minerals of which the chemical type is similar to that of 
 
 magnetite; but while, regarded as oxides, they are repre- 
 sented by the same typical formula, they have also some 
 claim to be regarded as oxygen-salts. 
 
 The first of this class is the Spinel group, which includes 
 spinel, magnetite, chromite and frankUnite, all of them 
 crystallising in the Cubic system. 
 
 Spinel in its transparent varieties is one of the precious Case lOef. 
 stones : the deep-red is the Spinel Buby (less dense and less 
 hard than the true Euby), the rose-tinted is the Balas Bvhy, and 
 the yellow or orange-red is the Buhicelle of the jewellers : some- 
 times, too, it has a dark blue colour. On account of their 
 hardness the less valuable specimens are used for the jewelling 
 of watches. Specially worthy of notice are a large polished 
 octahedron, and a small growth in which the twinning is repeated 
 in a peculiar way. 
 
 Spine] may also be regarded as an aluminate of magnesia : 
 varieties, chiefly opaque, are produced by the replacement of 
 the magnesia and of the alumina by other oxides ; among these 
 are wutomolite, dyslvdte, Icreittonite, and pleonaste. 
 
 Magnetite, or Magnetic iron ore, is the richest and most Case lofg. 
 valuable of the ores of iron, of which metal it contains 72 per 
 
and sesquioxides. 89 
 
 cent. Magnetite is one of the most widely occurring of minerals : 
 it is remarkable for its magnetic properties, and is found present- 
 ing polar characters : it is the natural loadstone. The crystals 
 from Nordmark and the Binnenthal are very bright and 
 sharply defined. 
 
 Cheomite is the corresponding oxide of chromium and iron : Case lOgh. 
 it is the chief source of the salts of chromium, which are 
 extensively used as dyes and pigments. 
 
 Franklinite is another member of this group ; it is first Case loh. 
 worked for zinc, and then the residue is treated as an iron ore. 
 
 Pitchblende consists almost entirely of oxygen and Case lOh. 
 uranium. From this mineral are obtained the uranium com- 
 pounds used in porcelain painting, and 'yielding yellow and 
 black colours. 
 
 Hausmannite has the same tj-pe of fbrmula as the members of case lOh 
 the Spinel group, and is an oxide' of manganese ; it crystal- 
 lises, however, in the Tetragonal system. 
 
 Cheysobeeyl belongs to this series of oxides ; it may also Case 9e. 
 be regarded as an aluminate of beryllium. In its trans- 
 parent varieties it is one of the precious stones : the beautiful 
 greenish-yellow variety, almost equal in lustre and hardness to 
 the sapphire, is the Oriental Clirysolite of the jewellers ; another 
 variety, with a peculiar play of light, is the true Cat's-eye ; while 
 a third, green by sunlight but red by candle- or lamp-light, 
 is the stone known as Alexandrite. Very fine twin-growths, 
 and cut specimens of these varieties, are shown in the case. 
 
 Scsqui- The next series is that of the sesqtdoxides. 
 
 oxides, Beaunite is the sesquioxide of manganese, and crystallises in Case 9/. 
 
 the Tetragonal system ; the specimens in the case from 
 
 San Marcel are unusually fine. 
 
 COBUNDUM is the sesquioxide of aluminium, and crystallises Case 9f-h. 
 in the Ehombohedral system. 
 
 Banking next in lustre and in hardness to the diamond, it is, 
 after the diamond, the most precious of stones. When pure 
 it is the colourless variety known to jewellers as the Imx Case 9h. 
 Sapphire: but with very minute traces of colouring ingre- 
 dient it assumes the richest hues; when red it is the true 
 
90 Sesquioxides 
 
 Hvhy ; when azure it is the SappMre ; while the yellow, green 
 and purple varieties are knqwn respectively to jewellers as the 
 Oriental Tofaz, Emerald and Amethyst; the prefix Oriental, 
 though at first used to suggest that the stones are not the 
 ordinary topaz, emerald and amethyst, but others of a similar 
 colour coming from the East (India, Ceylon, Siam, Pegu, &c.), 
 was afterwards understood to imply only the exoellence of their 
 characters. The Star-stones are a variety which, when placed 
 in a strong light, show a six-rayed star ; its position bears a 
 simple relation to the crystalline form. 
 
 An extensive suite of facetted specimens of these varieties will 
 be found in the case. 
 
 Emery is an opaque and impure corundum, but is still, from Case 9f. 
 its great hardness, very valuable as a polishing material. 
 
 HAEMATITE, though very dilBferent from corundum in its Case iia-i 
 extendi characters, corresponds to it very closely both in 
 chemical type and in the fundamental angles of the crystalline 
 form ; it is a sesquioxide of iron and a very important ore. 
 
 Of Specular iron, the crystallised variety of heematite, a 
 fine suite of specimens, more especially from Elba and Switzer» 
 land, is shown in. the case ; some of them have a characteristic 
 tarnish which produces an effect of great beauty. 
 
 The massive variety known as Bed Sasmatite is found in Case lia. 
 large deposits both in Lancashire and Cumberland ; a large 
 mass of it will be seen in a corner of the Pavilion. Bed Ochre 
 is an earthy variety of this mineral. Red Ochre, and also 
 massive haematite when reduced to powder, are used as polishing 
 materials. 
 
 lliMENiTE is one of the" ambiguoUB species of this series, and Case lid. 
 may be regarded either as an oxide of titanium and iron ' ' 
 analogous to hsematite, or as a titanate of iron. Its crystals 
 have almost exactly the same angles as those of hsematite ; 
 the proportions of the sesquioxides of iron and titanium in 
 ilmenite are very variable. It is the mineral in which the 
 element titanium was first discovered. Fine crystals, chiefly 
 from Eussia, are exhibited. 
 
 With this series are arrangcid the hydtated sesquioxides. 
 
 GotHiTfE is a hydrated sesqUioxide of iron ; unusually fine Case 12a. 
 
 crystals of this mineral are shown from the Eestomiel and 
 
 Botallack mines, Cornwall. 
 
and dioxides. 91 
 
 DiASPOEE is the corresponding compound of aluminium, and Case 12bc. 
 
 Manqaotte, that of manganese. 
 The last three minerals are very similar in their crystallo- 
 
 graphio as well as in their chemical type. 
 
 TxJEGiTE is a common ore of iron, containing, in addition to Case i2d. 
 the elements of ha3matite, 5 per cent, of water. 
 
 LiMONiTE is one of the most important ores of iron, and Case i2de. 
 when pure yields iron of superior quality ; it has the same 
 components as turgite, but contains about 15 per cent, of 
 water. Eeduced to powder it is, like hasmatite, used as a 
 polishing material. 
 
 LiMNiTE is the most highly hydrated oxide of iron, and Case i2f. 
 contains as much as 25 per cent, of water. 
 
 Beauxite, or Bauxite, a hydrated oxide of aluminium and Case i2f. 
 iron, is used for the manufacture of metallic aluminium on a 
 large scale. 
 
 PsrLOMELANE is a common ore of manganese, and generally Case i2fg. 
 contains from 70 to 80 per cent, of the oxides of that metal : 
 the oxide of barium present sometimes reaches 17 per cent. 
 
 Wad is a very similar mineral, but contains more water. Case i2h. 
 
 The last five minerals are not found crystallised. 
 
 Dioxides. pYEOLUSiTE, beginning the series of dioxides, is the most Case lie, 
 important ore of manganese. It is much used in the manu- 
 facture of glass for getting rid of the brown and green tints ; 
 also for bleaching purposes, and for the preparation of oxygen * 
 The sulphate and chloride of manganese made from it are used 
 in calico printing. Large and fine dendritic growths of 
 pyrolusite are met with in the limestone of Solenhofen, in 
 Bavaria; a good specimen is placed in the lower part of 
 case 14. 
 
 Cassiteeite, or Tia-stoiie, is the ore of tin, of which metal it Cas^s 
 contains 79 per cent. The mines of Cornwall supplied the 
 ancients with niuch of their tin. An extensive suite of 
 crystals from Cornwall, Sehlaggenwald and Ville d' Er will be 
 found in the case. 
 
 Wood-tin is an uncrystallised fibrous forln of the mineralj Case iSa; 
 somewhat like dry wood in colour and structure. 
 
92 Dioxides. 
 
 Stream-tin is the ore in the form of sand, as obtained from Case I3ab. 
 the beds of streams or the adjoining gravel. 
 
 Zircon contains the dioxides of both zirconium and silicon : Case I3bc. 
 its crystals belong to the same system as those of cassiterite, 
 and they have almost identical angles. Twin-growths are, 
 however, as rare in zircon as they are common in cassiterite: 
 the specimen from Eenfrew in Canada is remarkably fine. 
 When clear and without flaws it is one of the precious stones : 
 one variety with peculiar red tints is the Hyacinth or Jaeynth, 
 while the colourless, yellowish and dull green are termed 
 Jargoon : the colourless variety, owing to its high refractive 
 power, approaches even the diamond in brilliancy : zircon is the 
 heaviest of the precious stones. Fine cut specimens, and an 
 almost unrivalled suite of Eussian crystals, are shown in the 
 case. 
 
 Thorite has a similar composition to zircon, the zirconiTim Case 13c. 
 being here replaced by the rare metal thorium ; it contains 
 from six to nine per cent, of water, and is probably a result 
 of alteration. Orangite is a yellow variety of this mineral. 
 
 EuTiLE, Anatase and Bbookite are chemically identical. Cases 
 and are various forms of the dioxide of titanium. "' "' 
 
 Fine specimens of rutile from Titanium Mount and Brazil, of 
 anatase from Switzerland, and of brookite from North Wales 
 and the Zillerthal, will be found in the cases. 
 
 We now come to a large group of specimens illustrating the 
 manifold forms with which silica, the dioxide of silicon, 
 presents itself in the Mineral Kingdom. The group begins 
 with the crystallised varieties, tridymite and quartz, and 
 ends with the amorphous variety, opal. Between these are 
 arranged varieties regarded as mixtures of the crystalline 
 and amorphous with each other, or also with oxide of iron, 
 clay, or other impurities. 
 
 Teidymitb is a form of sUica remarkable as crystallising Case 14b. 
 in the Anorthic system, though the crystals are often 
 so twinned that the growths present Hexagonal symmetry. 
 It has the specific gravity of opal, which is less than that of 
 quartz. 
 
 Quartz in its clear and transparent variety is the Crystal of Case i4bc. 
 the ancients, and the Rock-crystal of modern times ; it is the 
 Brazilian Pebble of the spectacle-makers. Several of the 
 
Dioxides. 93 
 
 specimens from La Gardette are remarkable not only for their Case Ub. 
 clearness, but also as fine examples of a rare kind of twin- 
 growth. The simple rhombohedra from Bristol and Onega, and 
 the rare specimens showing a basal plane, are worthy of notice. 
 A large ball, brought from Japan, illustrates this species in its Case I4c. 
 purest form. The largest crystals are shown on separate 
 stands in the Pavilion : one of them, a fine well-developed 
 crystal, was presented in 1882 bv Mr. C. S. Bement, of 
 Philadelphia, U.S.A. 
 
 The history of the formation of rock-crystal is illustrated Case I4d. 
 by some most interesting specimens enclosing other minerals. 
 
 Next follow the less clear varieties of quartz, beginning Case I4e. 
 with the white. The Fotato-stone from Clifton, near Bristol, in 
 outer aspect is like its namesake, but when broken is found 
 to be hollow and lined with crystals. Cotterite, an Irish quartz, Case i4f. 
 has a peculiar pearly lustre. 
 
 To this succeed the smoky varieties, including the Scotch Case I4fg. 
 Cairngorm and Occidental Topaz. Next comes the Amethyst, Case i4gh. 
 sometimes yellow, sometimes purple ; as a precious stone the 
 latter lacks in brilliancy, but still is beautiful in colour. The 
 Amethyst is distinguished from the other varieties of quartz 
 by its rippled fracture and optical characters. Next follow 
 the Milky quartz, Rose-coloured quartz, and the Prase of a leek- Case ise. 
 green colour. Atfanturine quartz is the name given to a variety 
 spangled in general with mica. The Quartz Cat's-eye is a 
 variety presenting the opalescence, but not the hardness or the 
 brilliancy of the true Cat's-eye (chrysoberyl), an effect due to Case I3f. 
 fibres of an asbestos-lilce mineral in the specimens from Ceylon, 
 and to fibres of crocidolite in the blue, and of altered crocidolite 
 in the brownish-yellow specimens from South Africa. 
 
 These are followed by a series of specimens illustrating 
 peculiarities of form : cellular, hacked, spongy, fibrous (both 
 parallel and radiated), and capped. 
 
 The so-called Eisenkiesel, or iron-flint, encloses and is coloured Case i3g. 
 by the yellow or red oxide of iron. 
 
 Next comes Jasper, an uncrystallised coloured mixture of q^^^ i3-j,_ 
 silica and clay, distinguished from ordinary quartz by its 
 opacity and dull " earthy " fracture. It is of various colours, 
 chiefly red, brown, yellow and green ; and the colours are 
 
94 Dioxides. 
 
 arranged sometimes in a nodular form as in the Egyptian Cue I3h. 
 jasper, at other times in stripes, as in the Eiband jasper. 
 
 The LyMan- or Toueh-stone, by reason of its hardness and Case i5a 
 black colour, has been used from remote ages to test the purity 
 of the precious- metals. 
 
 Somsione is a variety of silica without evident crystallisation. Case i5a. 
 and generally presents a more or less splintery fracture ; but in 
 one kind, Flint, the fracture is conchoidal, sometimes conical, Case i5b. 
 as is well shown by the specimens in the case ; in Wood-stone Case I5a. 
 the particles of woody matter have been replaced by silica, 
 but so slowly that the details of the original structure have 
 been well preserved. 
 
 Chalcedony has a lustre nearly that of wax, and is either Case I5b-a, 
 transparent or translucent : specimens from the Trevascus and 
 Pednandrea mines, Cornwall, and from the Faroe Islands and 
 Iceland, are worthy, of special notice. The specimens from 
 Uruguay enclose water. 
 
 The Heliotrope, or Bloodstone, is a green gtone with red Case I6a. 
 blood-like spots. 
 
 Next follow the Plasma and Chrysoprase, green stones : and 
 the Sard, generally a brownish-red ; as also the Sardonyx, its 
 banded variety: all of them much prized by the ancients 
 because, though hard and tough enough to resist ordinary 
 wear and tear, they are more suited to tlife display of the 
 engraver's skill than are the harder and more precious stones. 
 
 Then come the Agates, chiefly formed of thin layers of porous Case I6b-e. 
 chalcedony of different colours, though the material of many 
 of the white layers is a compact semi-opal. Most of the 
 specimens are now brought from Uruguay, in South America, 
 and are cut and polished at Oberstein, where, in former times, 
 agates were got from the mountains of the district. Sometimes 
 the layers are plane and parallel, and the stone is then an 
 Owyx, useful as a material for cameos : or the bands of a section Case i6c. 
 are arranged in sets of straight but zig-zag lines, and the 
 stone is then called a Fortification agate : but in the ordinary 
 agate the layers are variously curved : many examples of the 
 variety of curve and colour will be seen in the case. The 
 Brecciated agate from Kunnersdorf is especially worthy of notice. 
 
 The Moss-agates, or Mocha-stones, are varieties of chalcedony, Ga»e XGe. 
 
Dioxides, &c. 95 
 
 enclosing moss-like forms of oxides of manganese and iron arid 
 green earthy chlorite. 
 
 The Camelian is a beautiful stone much valued by the Case I6e. 
 engraver : its fracture has a peculiar waxy lustre, and is distinct 
 from that of the sard, which is dull and hornlike. 
 
 We now come to the varieties of Opal, the first being Cases 
 Hyalite, its purest form, generally clear and transparent as glass. ~ ' 
 
 Next follows the Precious or Nohh Opal, conspicuous for its 
 fascinating play of colours : by the side of those from the old 
 Hungarian locality will be seen good examples from Queensland. 
 
 Hydrophane is remarkable as only being transparent and 
 opalescent when its pores are filled with water. 
 
 The Fire-opal, from Mexico, varies from hyacinth-red to Case I6g. 
 honey-yellow in colour. 
 
 Next to these are arranged other varieties, the green Prase- Cases 
 opal. Common opal, Bose-opal, Wood-opal, Liver-opal, Semi-opal, ' *' 
 Cacholong, and also Fiorite with its beautiful pearly lustre. 
 
 A series of specimens illustrating some of the forms of native 
 silica, arranged and described by Professor Euskin, is shown in 
 a table-case of the Pavilion. 
 
 Other acid- To quartz and opal, which terminate the series of the dioxides, 
 
 forming BTicceed some other acid-forming oxides. 
 
 oxides. Arsenolite Is the native sesquioxide of arsenic, crystallising Case 15f. 
 
 in the Cubic system ; the same compound artificially pre- 
 pared, is known in commerce as white arsenic or arsenions 
 acid, and is obtained on a large scale by roasting arsenical 
 ores. 
 
 Senabmontite, the isomorphons • sesquioxide of antimony, is Case I5f. 
 represented by fine specimens from Algeria. 
 
 Yalentinite has the same chemical composition as senarmon- Case 15g. 
 tite, but its crystals belong to the Orthorhombic system. 
 
 Sassoline is the hydrated sesquioxide of boron (native boracic Case 15g. 
 acid), found in the crater of Vulcano, one of the Lipari Islands. 
 
 Ceevantite is a peroxide of antimony, and is a product of Case I5h. 
 the decomposition of stibnite. 
 
 Section li. We next begin the section of oxygen-salts, the first class 
 
 — Oxygen- under which is formed by the carbonates. The long series 
 
 salts. of specimens of the anhydrous carbonates begins with those 
 
 of which the crystals belong to the Orthorhombic system. 
 
 Carbonates. 
 
96 Carbonates. 
 
 Aragonite is the calcium carbonate or carbonate of lime, and Casel7a-d. 
 is identical in cbemical composition with tbe mineral oalcite, 
 which crystallises in the Ehombohedral system. The 
 coralloidal variety from Eisenerz is well represented in the 
 case, and a large specimen of that variety will be found 
 on a table at the end of the Gallery. The twin-growths from Case 17 b. 
 Girgenti, Hungary and Bohemia, are unusually fine. 
 
 WiTHEEiTE is the barium carbonate ; it is mucb used in Case iSa. 
 the manufacture of plate glass, and, in France, for that of beet- 
 sugar: tbe specimens from Fallowfield mine are remarkable 
 twin-growths. 
 
 Stbontianite, the strontium carbonate, is the mineral from Case i8b. 
 which most of the strontium nitrate is made for use in the 
 manufacture of fireworks, owing to the fine crimson colour 
 which it gives to the flame ; it is at present much employed 
 in the process of sugar refining. 
 
 Ceeussite is the corresponding lead carbonate, and is Casei8b-d. 
 identical in chemical composition with the manufactured 
 " white-lead " of commerce : when abundant it is a valuable ore 
 of the metal. The suite of crystallised specimens is a very fine 
 one, but the specimens from Cardiganshire and PouUaouen, 
 presented by Mr. J. Taylor and Mr. E. Simmons respectively, case i8o. 
 are worthy of special mention. 
 
 The isomorphism of calcium, barium, strontium and lead, is 
 well shown by the above minerals, which are almost 
 identical in their fundamental angles. 
 
 Next follow the Ehombohedral carbonates : on account of the 
 isomorphism there is in several cases a gradual transition 
 from one species to another. 
 
 First of the Ehombohedral carbonates is Caloite. The cases 
 clearest and purest variety is that from Iceland, thence termed i8e-20c. 
 Iceland spar. In this variety, owing to its clearness, was first 
 remarked the fact that generally there are two images of an 
 object seen through a cleavage-plate : whence it is sometimes 
 called Double-refracting spar. It is largely used in optical 
 instruments for affording polarised light. 
 
 The extraordinarily fine suite of specimens of caleite ex- 
 hibited in the cases illustrates the almost endless variety of 
 its crystalline fofm, and at the same time shows that the 
 
Carbbnates. 97 
 
 variation is controlled by a definite law of symmetry. The 
 specimens from Derbyshire and Cornwall are particularly 
 worthy of attention. Two very large crystals from Iceland 
 are shown in the Pavilion. 
 
 Specimens of twin-growths are shown in case 19b. 
 
 The so-called Crystallised sandstone of Fontainehleau is a Case i9d. 
 curious variety of calcite enclosing a large quantity of grains of 
 sand. 
 
 In case 20a, are shoWn stalactites and stalagmites, formed 
 respectively on the roofs and on the floors or sides of caverns : 
 they owe their origin to the slow dropping and evaporation of 
 water, which has become charged with carbonic acid, and after- 
 wards with carbonate of lime, in its course through limestone rocks. 
 
 These are followed by a group of specimens illustrating the Case 20bc. 
 varieties of colour presented by this mineral. 
 
 Carbonate of lime occurs on a large scale as limestone and 
 marble, varieties which will be found among the Eocks. 
 
 Magnesite is the corresponding carbonate of magnesium. Case 20d. 
 
 Dolomite is a carbonate of magnesium and calcium. The Case 20d-f. 
 rock is used as an ornamental marble ; when burnt it yields 
 a durable cement. Both dolomite and magnesite were formerly 
 largely used for the preparation of artificial Epsom salts. 
 
 Ankerite contains the carbonates of calcium, magnesium and Case 20g. 
 
 iron. 
 Mesitite is the corresponding carbonate of magnesium and Case 20h. 
 
 iron. 
 
 Chalybite, or Spathic iron ore, is the carbonate of iron, Cases 
 and is a most valuable ore of the metal. The series of crystal- ^'^''^^^-g- 
 Used specimens from Cornwall is very fine. Mixed with clay 
 it is the most important English iron ore, Clay-iron-stone. 
 
 Ehodoceosite is the carbonate of manganese : it is affected by Case I9gh. 
 the action of light. 
 
 Calamine, the carbonate of zinc, is an important ore. The Cases 
 crystallised specimen presented by Mr. E. Simmons, in 1836, ^^^' ^^''' 
 is unique for excellence. 
 
 Barytocalcite is a carbonate of barium and calcium, remark- Case 21b. 
 able as crystallising in the Oblique system : a fine series of 
 specimens is exhibited. 
 
 a 
 
98 
 
 Silicates. 
 
 Hydrated 
 carbonates. 
 
 Carbonates 
 combined 
 
 with 
 
 chlorides, 
 
 &c. 
 
 Chessylite and Malachite are respectively the blue and Cases 
 green hydrated carbonates of copper, and are ores of that ' 
 metal. An excellent suite of specimens of chessylite will be 
 found in the case. Malachite is found in large masses; and by 
 reason of the high polish which it takes and its beautiful 
 markings, is much used for ornamental work of various kinds. 
 
 Ceomfoedite, or Phosgenite, a compound of carbonate and *^^sf '^'^^■ 
 chloride of lead, is represented by remarkable specimens 
 from Matlock, and from Monte Poni in Sardinia. 
 
 Paeisitk is a compound of the carbonates and fluorides of ^^'* '^'^ 
 cerium, lanthanum and didymium; the suite of crystals 
 from the Emerald mines of Muso is an extremely fine one 
 for this rare mineral. 
 
 Silicates. 
 
 Series i. — 
 
 Monoxide 
 
 bases. 
 
 The next class of oxygen-salts is that of the silicates, 
 occtipying no less than twelve cases. The minerals com- 
 prised in this large, varied and important class, are arranged 
 in series distinguished by the type of oxide that character- 
 ises the bases of the silicate ; in the first series are placed 
 the silicates corresponding to monoxide-bases (ferrous 
 oxide, magnesia, &c.) ; in the second, those of which the bases 
 are sesquioxides ; and in the third, the silicates of which 
 the bases are of both kinds. 
 
 The anhydrous section of the first series begins with the 
 orthosilicates. 
 
 A group of Ehombohedral minerals includes Willemitb, a Case 22e. 
 zinc silicate, and Phenakite, a di-beryllium silicate; ex- 
 tremely fine specimens of the latter mineral from the 
 Emerald mines of the Urals are shown in the case. Here 
 also is arranged Dioptase, fine crystals of which are now Case 22ef. 
 rarely met with ; it is a hydrogen-copper sUicate. 
 
 Passiag to the next group which consists of Orthorhombic 
 
 minerals,, we find Tepheoite a manganese silicate, and Case 22f. 
 Olivine a magnesio-ferrous silicate of the series. 
 
 Olivine in its clear transparent forms is one of the less 
 hard and least valued of the precious stones ; when of a yellow 
 colour it is known as the GIvrysolite, while the pistachio-green 
 variety is the Peridot of jewellery. Fine crystals and facetted 
 specimens are shown. 
 
 HuMiTE, a highly basic fiuo-silicate of magnesium, is arranged Case 22g. 
 here : the specimens are numerous and fine. 
 
Silicates, 99 
 
 GiDOUNiTE, also one of the more basic silicates, chiefly of Caso 22gh. 
 yttrium, iron and beryllium, is represented by fine crystallised 
 specimens, more especially from Hitteroe. 
 
 The minerals Enstatite, Beonzite and Hypersthene, crystal- Case 22n. 
 lising in the Orthorhombic system, begin the metasUicates ; 
 they are silicates of magnesium and iron, the relative pro- 
 portions of the metals varying in the different minerals. 
 
 The extensive Aiigite and Hornblende groups now follow ; Cases 
 though the chemical type is the same for all the members 2Xe-24c. 
 of these groups, the bases vary much both in nature and 
 relative proportion, and thus give rise to so many varieties 
 that we must refer the visitor to the text-books of Miner- 
 alogy for their discussion. 
 
 Spoddmene, essentially a silicate of aluminium and lithium. Case 23a. 
 is represented by very fine large specimens, one of the best 
 being shown in the lower part of the case ; a rare emerald- 
 green variety from North Carolina,U.S. A., Hiddenite, of which 
 both crystals and a clear facetted specimen are exhibited, 
 has been lately introduced into jewellery as a precious stone. 
 
 Ceocidolite is a sUicate of iron and sodium ; it is an asbestos- Case 24a. 
 like mineral, interesting as being the fibrous substance 
 enclosed in the Soiath African blue quartz cat's eyes. 
 
 Asbestos is the only variety of hornblende used in the Case 24c. 
 arts: it is found in long fibres, and in some of its varieties is . 
 so iiexible that it can be woven into gloves and other articles ; 
 examples will be found among the worked specimens in the 
 Pavilion. The term asbestos, nmquenched or imqiienchabh, was 
 applied to the mineral by the ancient Greeks because, owing 
 to its being unaltered by heat, wicks made of it were used 
 in maintaining the sacred perpetual fires of their temples. 
 Napkins of asbestos were cleaned by being thrown into the 
 fire ; asbestos cloth was also used in the process of cremation 
 to keep the ashes of the body distinct from those of the fuel. 
 It is now much employed for lining iron-safes, as a packing 
 for steam-pipes and boilers, and in gas-stoves. 
 
 .Jade, or Nephrite, is a mineral assigned to this group, and Case 24d. 
 is essentially a silicate of magnesium and calcium. This 
 mineral has few known localities, and it has been difficult to 
 answer the question as to whence the older workers of jade can 
 have obtained their material ; the prehistoric jade was got partly 
 
 G 2 
 
100 Silicates. 
 
 from China, partly from the Kuen Lun Mountains on the 
 northern border of Thibet; all the white comes from the 
 former country. 
 
 The various shades of colour, and the beautiful polish which 
 this tough mineral will take, are illustrated by specimens in 
 the case. The worked specimens from New Zealand, of which 
 there are several in the collection, are now rare. 
 
 On a table at the end of the gallery will be found a 
 large worked mass of an olive-green colour, brought to 
 England by Lieut.-General Kyd, and presented to the Trustees 
 in 1830 by Mr. Thomas Wilkinson. Both in shape and colour 
 it resembles the Ganges tortoise: it was found near Alla- 
 habad at the bottom of a tank or pond, into which it had 
 probably been thrown by its worshippers to prevent its falling 
 into the hands of the enemy. An immense waterworn mass 
 found some years ago near the graphite mines of M. Alibert, 
 to the west of Lake Baikal, in Asiatic Russia, is shown in the 
 Pavilion. 
 
 One of the characters useful for the recognition of jade is 
 its specific gravity : this is generally about 3-0 in the green, 
 and about 2*9 in the cream-coloured varieties. 
 
 WoLLASTONiTE is the calcium metasilicate. Case 24e. 
 
 Ehodonite, the manganese metasilicate, crystallises in the case 24ef. 
 
 Anorthio system ; the specimens of richer colour are in 
 
 EuBsia used for ornamental work. 
 Babingtonite has the same chemical type and crystallises in Case 24f. 
 
 the same system as rhodonite, but is a silicate of calcium, 
 
 iron and manganese ; it was formerly worked in Cornwall 
 
 as an iron ore. 
 
 Apophyllite belongs to the hydrated section of this series ; it Cases 
 is a hydrated silicate of calcium and potassium. Extraor- 24f-h, 23e, 
 dinarily fine specimens, got in blasting the rocks during 
 the construction of the Bombay and Poonah railroad, were 
 presented by Mr. J. J. Berkley, in 1860 ; most of them are 
 shown in a wall-case of the Pavilion. 
 Mebesohaum is the light soft porous mineral used for Case 23g. 
 tobacco-pipes : it is a hydrated silicate of magnesium. 
 
 Talc is another hydrated silicate of magnesium, and was Case 23gh 
 formerly used in the manufacture of porcelain. The 
 amorphous form, steatite or soapstone, is worked by the 
 
Silicates. 101 
 
 » 
 
 Chinese into ornaments, of which examples are shown in 
 the Pavilion; it is also used for gas-humers, electric 
 insulators, linings for stoves, &c. 
 
 Serpentine is another hydrated magnesium silicate: the Case 25a. 
 ease with which it is worked and takes a good polish, its green 
 colour and varied markings render it much sought for as a 
 material for fire-places, tables, and other indoor work : exposed 
 to the weather it soon loses its polish. Occurring on 
 a large scale, it is best considered among the Kocks ; only 
 specimens illustrating the simple mineral are shown in the case. 
 
 Hkmimorphite, a hydrated silicate of zinc, is an important ore. Case 25b. 
 Chrysocolla is a hydrated silicate of copper. Case 25c. 
 
 oxide bases. 
 
 Series ii.— The second series, consisting of minerals in which the bases 
 
 ?ii- are sesquioxides, commences with topaz, a silicate of 
 
 aluminium, containing also a considerable percentage of the 
 element fluorine. 
 
 Topaz in its clear varieties is one of the precious stones. A Cases 
 large series of specimens illustrating the varieties of crystalline "^ 
 form will be found in the case ; those from the Urulga river in 
 Siberia are remarkably fine examples of crystalline develop- Case 25d. 
 ment; they are of a delicate brown colour, but are kept 
 covered up as the action of light speedily bleaches them. The 
 yellow crystals from Brazil assume a peculiar pink colour when 
 heated, and are then known to jewellers as Burnt or Fitik topaz ; 
 some of these will be found in case 26a ; crystals with the same 
 tint are sometimes found in Nature. The crystals from Saxony 
 are of a paler yellow colour, which they entirely lose on being Case 25c. 
 heated. Topaz has a very easy cleavage, and readily becomes 
 electric on being rubbed or heated. 
 
 Andalusite is a silicate of aluminium. Some of its transparent Case 26b, 
 crystals are very dichroic, as is well shown by a facetted 
 specimen in the case. 
 
 Staueolitb is a silicate, the bases of which consist essentially of Case 26c. 
 the sesquioxides of aluminium and iron ; it is remarkable for 
 its twin-growths, and is found almost exclusively in clay- 
 slates and mica-schists. 
 
 Kyanite has the same chemical composition as andalusite, but Case 26cd.- 
 crystallises in the Anorthic instead of the Orthorhombic 
 
102 Silicates. 
 
 system. The specimen from Chesterfield, Massachusetts, is Case 26d. 
 unusually fine-. 
 FiBROLiTE also has the same chemical composition. Being Case 26d. 
 extremely tough and yet not difficult to work, it was 
 manufactured into stone implements in prehistoric times, 
 particularly in parts of Prance. 
 
 Series iii.— '^^® third series of silicates is constituted of those in which 
 Monoxide monoxides and sesquioxides together act as hases. 
 
 and sesqui- First of these is the Garnet group, the members of which 
 oxide bases. ^11 crystallise in the Cuhic system hut vary indefinitely in 
 
 chemical composition, though always in accordance with 
 
 a definite typical formula. 
 
 Gaknet belongs to the group of precious stones ; when the Case 26e-h. 
 red is tinged with violet, it is the Almcmdme and the Syricm 
 garnet (from Syriam in Pegu), and when cut en cdboehon, the 
 Carhvmde of jewellery (Case 26f) ; the Ciwiamon stone or Essondte 
 is yellow (Case 26e) ; the Pyrope and the Bohemicm garnet are 
 blood-red (Case 26h^. Uwa/rowite is a green chrome-garnet 
 (Case 26h). In the case will also be found some of the green 
 garnets from the gold washings of the river Bobrowska, in Eussia 
 (Case 26a). Garnet often acts on the magnetic needle ; it is 
 one of the heaviest and most common of the precious stones. 
 
 Idocease crystallises in the Tetragonal system ; though Case 25ef. 
 
 essentially a silicate of calcium and aluminium, the 
 
 percentages of iron and magnesium in its difierent varieties 
 
 are sometimes very high. 
 SAECoutE also crystallises in this system, and is noticeable as Case 25g. 
 
 representing a kind of hemihedry of which there are few 
 
 examples. In addition to the elements of idocrase it 
 
 contains sodium. 
 ScAPOLiTE also is Tetragonal in its symmetry ; like idocrase it Case 25gh. 
 
 is a silicate of calcium and aluminium. 
 Lievei'Te is a silicate of calcium and iron, the latter element Casd 27a. 
 
 being present both as monoxide and sesquioxide ; a series 
 
 of good crystals from Elba is exhibited. 
 
 Jadbite is essentially a silicate of sodium and aluminium^ Case 27abi 
 It is one of the green stones which, under the name of jade, 
 are wrought into ornaments in China; from that mineralj 
 however, it is distinguished by its chemical composition, 
 structure and higher specific gravity, the latter ranging from 
 3-1 to 8-4. 
 
Silicates. 103 
 
 Epidote is essentially a silicate of calcium, iron and Case 27cd 
 alnminium. Fine specimens from the Untersulzbachthal are 
 in the case. 
 
 DiCHEOiTE is a silicate of magnesium, iron and aluminium ; case 28a. 
 its transparent variety is the SapMr d'eau of jewellery, 
 and is remarkable for the variation of its colour according 
 to the direction in which it is looked through ; the polished 
 specimens in the case illustrate this character. 
 
 MiOA is the name given to a group of minerals differing 
 much from each other in chemical composition and optical 
 properties, but having as a common character an easy cleavage 
 in a single direction, and thus affording plates remarkably 
 thin, transparent, tough and elastic. One of these nainerals, 
 muscovite, has been used in Russia in place of glass for 
 windows ; it is now in common use for lanterns and stoves, 
 not being so easily cracked as glass by change of temperature : 
 it is still known in commerce as talc, a term applied to it 
 by the older mineralogists. 
 
 In the Micas the oxides of potassium and aluminium are almost 
 
 invariahly present ; phlogopite contains a considerable q^^ 28a. 
 proportion of magnesium ; biotite contains both magnesium ^ oshc 
 and iron ; LEProoMELANE much iron and little magnesium, ^^^ ggc ' 
 much of the aluminium being replaced by iron ; asteo- ^ „. " 
 PHTLLITE contains much titanium, zirconium, &c., and little 
 aluminium ; Muscovite, much potassium and aluminium ; p, „„ , 
 LEPIDOLITE contains small proportions of lithium, rubidium „ „. 
 and caesium, and is an important source of lithixun and 
 rubidium salts. 
 
 Leucite is a potassium-aluminium silicate : its crystals were 
 long regarded as presenting typical forms of the Cubic ^^^ ^^^ 
 system, but vom Eath has, after minute examination, shown 
 that the symmetry is really that of the Tetragonal ; Klein 
 has lately discovered that its optical characters indicate a 
 sudden change to Cubic symmetry at a temperature probably 
 below the melting-point of zinc. A very fine transparent 
 crystal will be seen in the case. The mineral has only been 
 found in volcanic rocks. 
 
 Nepheline is a silicate of sodium and aluminium with some Case 28f< 
 potassium ; its crystals present Hexagonal symmetry. 
 
 We now come to the group of Felspars, the most important of 
 rock-forming minerals ; for details of their characters we must 
 refer the visitor once more to the text-books. Their crystals, 
 though belonging to two different systems, the Oblique and 
 Anorthic, present a great similarity of form ; they have two 
 
104 Silicates. 
 
 BAsy cleavages, at right angles in tlie Oblique and nearly bo 
 
 in the Anorthic crystals ; they are a little less hard than 
 
 quartz. The metals of the monoxide hases are calcium, 
 
 sodium, potassium, and in one species barium ; the sesqui- 
 
 oxide is that of aluminium. 
 Anorthite, represented by excellent crystals from Vesuvius Case 28f-h. 
 
 and other localities, is a lime-felspar. 
 Labradoeite is a lime-soda felspar, and is remarkable for Case 28h. 
 
 the change of colour of the light reflected from it in 
 
 different directions. 
 Oligoci-ase is a soda-lime felspar ; a superb crystallised Case 27e. 
 
 specimen from Switzerland is shown in the case. 
 Oethoclase, an Oblique potash-felspar, is represented by a Case 27e-h. 
 
 series of very fine specimens. 
 MicEOCLiNE is an Anorthic potash-felspar, closely simulating Case 29a. 
 
 orthoclase iii crystalline form. Amazon-stone is a green variety 
 
 of this mineral ; its colour is destroyed on heating. 
 Albite is a soda-felspar : PericUne, one of its varieties, is Case 29ab. 
 
 represented by very fine specimens. 
 
 Leaving the Felspar group we now come to beryl, a silicate 
 of aluminium and beryllium, presenting Hexagonal symmetry. 
 
 Emerald, its bright green variety, is one of the most valued Case 29c. 
 of precious stones. It was in ancient times worked in Egypt, 
 as is proved by the rough specimens found in the old workings 
 by Sir Gardner Wilkinson and presented by him to the Museum. 
 Emeralds are found in the Urals ; but the locality for the finest 
 stones has for a long time been that of Muso, about seventy 
 miles from Santa Fe de Bogota, in S. America ; excellent 
 specimens are shown in the case. Lately emeralds, though 
 not of a very good colour, have been discovered in the United 
 States ; some of the best of those found are here shown. 
 
 The remaining varieties of this species are illustrated by a Cases 
 large suite of crystals, those from Mursinsk, in the Urals, being 29c-30a. 
 particularly fine. Facetted specimens of the colourless beryl, 
 and also of the bluish-green beryl, known in jewellery as 
 Aquamarine, are exhibited. 
 
 EucLASE is a silicate of aluminium, beryllium and hydrogen, and Case 30b. 
 crystallises in the Oblique system : a fine, almost unique, 
 suite of crystals of this rare mineral is exhibited. Attempts 
 have been made to introduce this mineral into jewellery on 
 account of its lustre and hardness ; but for this purpose 
 its brittleness and easy cleavage make it unsuitable. 
 
Silicates. 105 
 
 We now come to the remaining hydrated silicates, tlie first 
 
 series of ■whicli consists of those minerals in wMcli the 
 
 hases are sesquioxides. 
 In this series are the various hydrated silicates of aluminium, 
 
 including kaolinite, halloysite, the unsatisfactory group of 
 
 clays, pyrophyllite, &c. 
 Kaolinite is a result of decomposition of the felspar of granite, Cas« 30b. 
 
 and, under the name of China-clay, the mixture of kaolinite and 
 
 quartz is extensively used for the manufacture of porcelain. 
 As a first group in the series of hydrated silicates having 
 
 both monoxides and sesquioxides for hases, we come to the 
 
 Zeolites, so called because when fused they appear to hoil, 
 
 owing to the escape of the water. 
 Prehsite has for bases alumina and lime ; the proportion of Case 30cf. 
 
 water is only about 4-4 per cent. 
 Natrolite has for bases alumina and soda ; in lyiESOLiTE the Case BOgh. 
 
 soda is partly, and in Scolecite wholly, replaced by lime : Case 29ef. 
 
 fine specimens from Iceland and India are shown. 
 Edixgtonite is a hydrated silicate of aluminium and barium ; Case 29g. 
 
 it is an exceedingly rare mineral, and has only been found 
 
 as small crystals in the amygdaloid of the Kilpatrick Hills, 
 
 near Glasgow. 
 Analcime has for bases alumina and soda ; the specimens of Case 29gh. 
 
 this mineral famish very typical examples of the symmetry 
 
 of the Cubic system. 
 PoLLuciTE is remarkable as being a hydrated sUicatQ of alu- Case 29h, 
 
 minium and of the rare element caesium ; the water amounts 
 
 to only 2 ■ 4 per cent. 
 Laumontite has for bas.es alumina and lime ; exposed to dry Case 29h. 
 
 air the specimens fall to powder, owing to loss of water. 
 Chabasite has the same bases as laumontite ; its crystals. Case 3ib. 
 
 though really belonging to the Ehombohedral system, are 
 
 almost cubical in form. 
 Harmotome, a hydrated silicate of aluminium and barium, is Case 31d. 
 
 represented by very fine specimens from Strontian and 
 
 Andreasberg; the cruciform growths of this mineral are 
 
 very characteristic. 
 Stilbite and Heuxandite are also hydrated silioates, having Case 32a-d. 
 
 for bases alumina and lime, and crystallising respectively in 
 
 the Orthorhombio and Oblique systems ; an exceedingly fine 
 
 suite of specimens from Iceland, Faroe Is. and India, is 
 
 shown in the case. 
 
 We now leave the Zeolites and come to the Chlorite group, 
 the members of which are very similar to the Micas in 
 their general characters, but have water in their compo- 
 sition. 
 
 Pennine, has for bases alumina and magnesia, with some Case 32e. 
 oxide of iron. Its crystals are Rhombohedral in symmetry. 
 
106 
 
 Silicates. 
 
 Silicates 
 combined 
 
 with 
 sulphides, 
 chlorides, 
 ' &c. 
 
 Silicates 
 combined 
 
 with 
 boiatesi 
 
 Veemiculite is a name given to a series of minerals wHch. Case 32e. 
 possess the curious property of exfoliating when heated, 
 the volume being thereby increased sometimes as much as 
 tenfold. 
 
 Clinochlore has a very similar composition to pennine, but its Case 32f. 
 crystals are proved by their optical characters to belong to the 
 Oblique system; a superb specimen from Achmatovsk is 
 exhibited. 
 
 KiPiDOLiTE has the same components as pennine and cHno- Case 32g. 
 chlore, but contains a large percentage of the monoxide of 
 iron, and possibly belongs to the Khombohedral system. 
 
 Margaeite is a hydrated silicate of alumina and lime. Case 32h. 
 
 Leaving this group, and at the same time the hydrated 
 
 aluminium silicates, we come to 
 Ceonstedtite, a hydrated silicate having for bases the sesqui- Case 3le. 
 
 oxide of iron, and the monoxides of iron and manganese : 
 
 unusually well crystallised forms of this Ehombohedral 
 
 mineral are in the case. 
 These are succeeded by a series of uncrystallised silicates of Case 3lfg. 
 
 more or less uncertain composition. 
 
 Leaving .the silicates proper, we next come to minerals 
 
 containing silicates in combination with other compounds, 
 
 the latter containing no oxygen. 
 Danaiite and Helvine are compounds of silicates with Case 31gh. 
 
 sulphides. 
 SoDALiTE is a sodium-aluminium silicate combined with 'sodium Case 31h. 
 
 chloride ; it crystallises in rhombic dodecahedra. 
 Pyeosmalite is a silicate of iron- and manganese, containing Case 31h. 
 
 also chlorine and water ; a fine suite of specimens will be 
 
 found in the case. 
 
 These are succeeded by mineralB in which silicates are 
 
 associated with other compounds of oxygen. 
 First are arranged the minerals in which sUicates are associated 
 
 with boric-oxide or borates. 
 
 ToBEMALiNB is a mineral of which the crystals belong to the Case 33a-c. 
 Ehombohedral system, and are remarkable as presenting a 
 difference in the development of the faces at the two ends of 
 the prism, This difference in the crystalline development of 
 the two ends is accompanied by a difference in electrical 
 behaviour ; for when a crystal of tourmaline is being warmed 
 or cooled, not only does it become electric and first attract and 
 then repel lighit bodies in the same way as does amber, but one 
 end of the crystal is opposite in electrical character to the 
 other. Tourmaline of certain colours is much valued for its 
 
Silicates combined with other salts. 107 
 
 property of acting as a polariser on common light, a plate of 
 the proper thickness absorbing one of the two rays produced 
 by the double refraction. Tourmaline is very variable in 
 colour and also in chemical composition. 
 
 Some of its varieties when free from flaws are classed with 
 the precious stones. Among these is the pink variety called 
 Biibellite. Two very fine specimens of rubeUite from Ava Case 33a. 
 are shown in the case ; one of them, remarkable for its size and 
 shape, was brought from that country by Colonel Symes to 
 whom it had been presented by the King ; the other, not so large 
 but of a deeper colour, was presented in 1869 by Mr. C S. 
 J. L. Guthrie. On a table in the Pavilion will be found a 
 specimen from Elba, showing a large group of pink crystals 
 still attached to the rock. , 
 
 The pink-and-green tourmalines from Paris, Maine, U.S. A., Case 33a. 
 are among the more beautiful of the mineral products of the 
 United States. 
 
 AxiNiTE is a borosilicate, with alumina as the sesquioxide, and Case 33d. 
 lime and ferrous oxide as the monoxide bases ; the suite of 
 specimens is unusually fine. 
 
 Daitbueite and Datholite are borosiHcates of calcium, the Case 34a. 
 latter containing about 5 ■ 6 per cent, of water : worthy 
 of special mention are the specimens of Danburite from 
 Berg Scopi, and of Datholite from Toggiana and the Harz. 
 
 Silicates BLiiJTNE is a compound silicate and sulphate having for Case 34b. 
 
 ^"'•th"^ monoxide bases soda and lime, and for sesquioxide base, 
 
 sulphates, alumiuaj the rich blue variety is the Lapis Lazuli of jewellery, 
 
 and is brought from Persia, China, Siberia and Bokhara^ 
 
 generally in the massive state. A large crystal in the case 
 
 is worthy of attention. 
 
 When powdered, lapis lazuli furnished the once costly 
 pigment ultramarine; through the discovery of a method of 
 producing an artificial and cheap form of the saine material, 
 the use of the mineral as a pigment has been quite superseded. 
 
 Titanates) ^® next come to a series of minerals not only themselves of 
 
 S:c. rare occurence, but having in several cases for constituents 
 
 some of the rarest elements, namely the titanates, tanta- 
 
 lates, niobates, zirconates, &c., both singly and in association 
 
 vdth. each other, and with silicates; 
 
108 
 
 Molybdates and tungstates. 
 
 Among these we may call attention to the specimens of Perof- Case 34c-h. 
 
 SKITE, TSCHEFFKINITE, EuDIALYTE, SpHENE, CoLUMBITE, SamARS- 
 
 KiTE, Fergusonite, Pyrkhitb and ^schynite, as teing 
 especially remarkable either for their excellence or their 
 rarity. 
 
 Jlolybdates 
 
 and 
 tungstates. 
 
 The next class is that of molyhdates and tungstates. 
 
 WuLFENiTE is the molybdate of lead, and is represented by Case 33ef. 
 fine specimens from the United Stat,e8 and Carinthia. 
 
 ScHEELiTE and Stolzite are respectively the tungstates of Case 33fg. 
 calcium and lead ; of scheelite a fine suite, including speci- 
 mens from Cumberland and Devon, is shown. 
 
 Wolfram is the tungstate of iron and manganese, and is the Case 33h. 
 chief source of the tungstates of commerce. 
 
 Chromates Croooisite is a mineral belonging to the next claes, and is a case 35a. 
 
 and chromate of lead ; it has the same chemical composition as 
 
 sulphates. ^^ artificial pigment chrome yellow. As this mineral is 
 
 affected by the light, the fine series of specimens from 
 
 Beresovsk and Brazil is kept in the drawers. 
 Anhydrite is the anhydrous sulphate of calcium. The crystal Case 35bc. 
 
 from Hallein is an exceptionally good one. 
 Celestine is the corresponding sulphate of strontium ; rare Case 35cd. 
 
 blue crystals from Hungary, and excellent specimens from 
 
 Bristol and Sicily are in the case. 
 Barytes, or Heavy spar, is the sulphate of barium ; it is a very ca«e 36a-d. 
 
 heavy mineral, being 4^ times as heavy as its own volume of 
 
 water. The suite of specimens from British localities is very 
 
 fine, and pre-eminently so are those from Wheal Mary Ann. A 
 
 remarkably clear specimen from Przibram wiU also be found case SGc. 
 
 in the case. The mineral is ground up and mixed with 
 
 white lead for use as a paint; barium sulphate is also 
 
 manufactured on a large scale for the same purpose and is 
 
 then known as permanent white. 
 Anglesite, the sulphate of lead, is represented by fine specimens Case 3fief, 
 
 from Anglesey and Derbyshire, and also from Pennsylvania 
 
 and Monte Poni. 
 Lanakkite also is a sulphate of lead ; the specimens in the case Case 36f. 
 
 are amongst the finest known of the species. 
 
 We now pass on to the hydrated sulphates. 
 
 Hydratcd Selenite, ot Gypsum, Is the hydrated sulphate of calcium. Case 36f-h. 
 
 sulphates, j^g crystals belong to the Oblique system ; by reason of the easy 
 cleavage parallel to the plane of symmetry it may be obtained 
 in very thin plates, which are much used in polarising apparatus. 
 
Chromates and sulphates. 109 
 
 Selenite, when lieated, gives up its water of crystallisation and 
 falls to a powder, known as " Plaster of Paris ; " when 
 moistened the powder combines again with the water and 
 forms a coherent solid. Fine specimens from Bex and Sicily 
 are in the case, and a very large crystallised specimen from 
 Eeinhardsbrunri in Gotha, a gift from H.R.H. the late 
 Prince Consort, will be found in the Pavilion. Gypseotis Case 36h. 
 alahaster is a massive variety of selenite ; owing to its white- 
 ness, fine texture and softness, it is largely used as a material 
 for statuettes and other ornaments ; the Oriental alahaster is a 
 harder substance, stalagmitic calcite. 
 
 Epsomite is the hydrated sulphate of magnesium, and is Case 36h. 
 known in commerce as Epsom salts : it is largely used in 
 medicine and in dyeing. Epsom salts are now largely manu- 
 factured from 
 
 KiESEBiTE, another hydrated sulphate of magnesium, which Case 36h. 
 occurs in beds at Stassfurt ; it is only slightly soluble in water. 
 
 Melanteeite is a hydrated sulphate of iron. The iron Case 35e. 
 sulphate of commerce (green vitriol), largely used for dyeing 
 and tanning, and for the manufacture of ink and Prussian blue, 
 is chiefly manufactured from pyrites and pyrrhotite. 
 
 Chalcanthite is a hydrated sulphate of copper. The Case asfg. 
 ' Blue Copper,' or ' Blue Vitriol ' of commerce is chiefly manu- 
 factured from copper turnings and roasted copper ores ; it is 
 much used in dyeing and calico printing. 
 
 Beochantite, Waeingtonite and Langite are also hydrated Case 35g. 
 
 sulphates of copper. The crystals of langite from Botallaek 
 
 and Fowey Consols are twinned like those of aragonite. 
 Lettsomite, a beautiful velvet-like mineral, is a hydrated Case 35h. 
 
 sulphate of copper and aluminium : remarkable specimens 
 
 are shown. 
 Alum, a hydrated sulphate of potassium and aluminium, has Case 37a. 
 
 long been valuable for dyeing purposes. The greater part 
 
 of the alum required for commerce is, however, obtained 
 
 artificially from alumstone and shale. 
 Alunite, or Alumstone, is another hydrated sulphate of these Case 37a. 
 
 metals: it occurs at the famous mines of Tolfa, in the 
 
 neighbourhood of Eome, and from it a very pure alum is 
 
 prepared by repeated roasting and lixiviation. 
 LiNAEiTE is a hydrated sulphate of lead and copper : Case 37b. 
 
 splendid specimens from Koughten Gill are exhibited. ■ 
 
110 Borates and nitrates. 
 
 Sulphates CoNNELLiTE is a compound of sulphate with chloride . of Case 37b. 
 
 combined copper. 
 
 with other Caledonite is a compound of sulphate of lead with the Case 37bc. 
 
 carbonates of copper and lead. 
 Leadhillitb and Susannite are compounds of sulphate with Case 37c. 
 
 carbonate of lead. 
 The specimens of the last five minerals shown in the case are 
 amongst the finest known. 
 
 Borates, LuDWiGiTE is a borate of iron and magnesium, and is very Case 37c. 
 
 similar in appearance to the dark-coloured fibrous tour- 
 maline. 
 Ehodicite, an extremely rare mineral, is probably an alkaHne Case 37c. 
 boro-aluminate : it was found near Ekaterinburg as minute 
 crystals on rubeUite. 
 
 Hydrated BoBAX is a hydrated borate of sodium. It is much used as Case 37c. 
 
 borates. ^ ^y^s., also in the process of soldering, and in the preparation 
 of easily fusible enamels. It was formerly carried over the 
 Himalayas from a lake in Thibet, but is now extensively 
 prepared from the boracic acid of the lagoons in Tuscany. 
 Fine crystals are exhibited from the Borax Lake of California, 
 which supplies the whole of the United States with borax. 
 
 Borates BoKACiTE is a borate of magnesium combined with chloride of Case 37d. 
 
 combined magnesium, the proportion of the latter amounting to 11 per 
 
 , ,y*^, cent. On account of its remarkable electrical and optical 
 
 &c. °^' properties, and the relation of these to the crystalline form, 
 
 boracite has long been extremely interesting to the mine- 
 ralogist. 
 
 Nitrates. NiTBE, or Saltpetre, the nitrate of potash, belongs to the Case 37d. 
 class of nitrates. It is used in the manufacture of gunpowder, 
 and of nitric and sulphuric acids, 
 
 NiTEATiNE, or Soda nitre, is the nitrate of soda : in the Case 37d. 
 Desert of Atacama it is found in beds extending for many miles. 
 It is used for the preparation of nitric acid and of saltpetre. 
 
 Phosphates, We now Come to the minerals which contain phosphates, 
 
 arsenates arsenates and vanadates ; nearly all are hydrated. 
 
 *°'\ Haidingerite and Phakmacolite are hydrated arsenates of Case 38b. 
 
 vanada es. calcium ; the Specimen of the former mineral, from the 
 
 Allan-Greg collection, is unique. 
 
Phosphates, arsenates and vanadates. Hi 
 
 Chuechite is a hydrated phosphate of cerium and didymium : Case 38b. 
 of this rare mineral one of the specimens in the case is the 
 finest known. 
 
 Ehabdophane, a blende-like mineral, to which attention was Case 38b. 
 first called by Mr. W. G. Lettsom, is a hydrated phosphate 
 of cerium, lanthanum, didymium and yttrium. Its pre- 
 cise Cornish locality is unknown ; the same mineral has 
 been lately discovered at Salisbury, Conn. U.S.A., and 
 described under the name Scovillite. 
 
 ViviANiTE is a hydrated phosphate of iron : a fine series of Case 38bc. 
 crystals is shown from Wheal Jane : it is sometimes found 
 with fossil shells and bones, having been a result of the 
 decomposition of the organic matter. 
 
 Erythrite is a hydrated arsenate of cobalt, found in beautiful Case 38o. 
 crystals. 
 
 Phaemacosiderite and Scoeodite are hydrated arsenates of Case 38de. 
 iron : an excellent suite of each of these minerals is 
 shown. 
 
 Wavellite is a hydrated phosphate of aluminium. Case 38ef. 
 
 Andeewsite is a hydrated phosphate of iron and copper : those Case 38g. 
 in the case are almost the only specimens known. 
 
 Calaite, or Turquoise, is a hydrated phosphate of aluminium ; Case 38g. 
 it owes its blue or green colour to the presence of small 
 quantities of salts of copper and iron. It does not occur 
 cryBtallised. Being as hard as felspar and taking a good 
 polish, it has been much prized in jewellery under the name 
 of Oriental Twqtwise; that which comes into the market is 
 chiefly brought from the turquoise mines, not far from Nishapur 
 in Persia. A fine large mass from a mountainous district in 
 China is shown in the case. Some specimens of the turquoise 
 found by Major Macdonald in the neighbourhood of Mount 
 Sinai are exhibited. 
 
 LiBETHENiTE is a hydrated phosphate, and OLiVENrrE the Case 37ef. 
 
 corresponding arsenate of copper. 
 LuDLAMiTE is a hydrated phosphate of iron : an unrivalled Case 37g. 
 
 suite of specimens from "Wheal Jane, its only certain 
 
 locality, is shown. 
 Clinoclase, a hydrated arsenate of copper, is represented by Case 37h. 
 
 good specimens. 
 Eeinite also is a hydrated arsenate of copper : of this Case 37h. 
 
 rare species a fragment of the only example known is 
 
 exhibited. 
 Chalcophyllite is another hydrated arsenate of copper ; fine Case 37h. . 
 
 examples are in the case. 
 
Phosphates, 
 
 iic, 
 
 combined 
 
 with 
 
 chlorides, 
 
 &c. 
 
 112 Phosphates, arsenates and vanadates. 
 
 Lazulite is a hydrated phosphate of aluminium and mag- Case 39b, 
 
 nesium : the Bpecimens from Werfen and Graves Mt. are 
 
 worthy of special notice, 
 Calco-ueaotte is a hydrated phosphate of uranium and calcium, Case 39o. 
 
 and is represented by very fine specimens from St, 
 
 Symphorien, 
 TJeanociecite is a similar compound in which the calcium is Case 39c, 
 
 replaced by barium : the fine Falkenstein specimen in the 
 
 case was presented by Mr, A. H, Church in 1881. 
 In CuPEO-UEANiTE the calcium is replaced by copper : the Case 39d. 
 
 Cornish suite is an excellent one. 
 Childeenite is a hydrated phosphate of aluminium, iron and Case 40a. 
 
 manganese : a remarkably fine suite, including the largest 
 
 crystal known, is in the case. 
 LiEOCONiTE is a hydrated phosphate of aluminium and Case 40a. 
 
 copper. 
 
 The next group is composed of minerals in the constitution of 
 which phosphates, arsenates and vanadates, are associated 
 with chlorides or fluorides. 
 
 Apatite is a mineral in which phosphate of calcium is Ca»e 40b-d. 
 associated with chloride or fluoride of the same metal. Among 
 the remarkably fine crystals exhibited may be specially men- 
 tioned those from Kiriabinsk, Knappenwand, Schwarzenstein Case 40c. 
 and Bovey Tracey, the best specimens from the latter locality 
 being in the lower part of the case. Phosfhorite, Somhrerite Case 40d. 
 and Osteolite are massive varieties of apatite. When abundant 
 it is valuable as an agricultural manure ; when used for this 
 purpose it is first treated with sulphuric acid. 
 
 Pyeomoephite is a coiTesponding compound in which the Case 40ef. 
 calcium is replaced by lead; and Mimetes:te has a similar Ca3e40gh. 
 constitution to that of pyromorphite, the phosphoric acid 
 being replaced by arsenic acid : excellent suites of both 
 these minerals are shown, but the specimen of mimetesite Case 40g. 
 presented in 1836 by Mr. Simmons is an extraordinary one. 
 
 Vanadinite is the corresponding vanadate of lead, and is also Case 39?. 
 represented by a remarkable series of specimens. 
 
 Wagnerite is a phosphate and fluoride of magnesium. Case 39e, 
 
 Oxalates. Whewellite, a hydrated oxalate of lime, is represented by a Case 39 h. 
 
 portion of what was long the only specimen known : the 
 crystals of whewellite are small and associated with crys- 
 tallised calcite. It was presented by Mr. W. G-. Lettsom in 
 1870. The mineral has been recently found near Dresden, 
 
( 113 ) 
 
 SUPPLEMENT. 
 Organic Compounds. 
 
 As a supplement to the collection of simple minerals, there is 
 arranged, in cases 41 and 42, a group of natural substances 
 which either belong or are closely related to the Mineral 
 Kingdom, although in their formation organised matter has 
 played a very important part. Consisting as these substances 
 do, either wholly or in part of carbon and hydrogen, they form 
 a group sometimes known as that of the Hydro-carbons. 
 
 The most important members are coal and amber. 
 
 Coal, in most of its varieties, gives structural evidence of its Case 4lab. 
 vegetable origin : its chemical composition depends on the 
 more or less complete nature of the change which has taken 
 place, and is thus not so definite as in the minerals of the 
 preceding divisions. In the variety called anthracite all 
 traces of the original organised structure have disappeared. 
 
 Ambee, in ancient times regarded as one of the precious case 42cd. 
 stones, is likewise of vegetable origin. It is a fossilised resin, 
 chiefly derived from trees analogous to the present pine : its 
 originally viscous condition is sufficiently proved by the insects 
 which are sometimes found enclosed in it. Some of the ambers 
 from Sicily shown in the case, when placed in the sun-light, 
 present in a remarkable degree the peculiar optical character 
 termed fluorescence. 
 
 «:-<^-<S>«■^Jfcg>''c^^-^^-' 
 
( 114 ) 
 THE PAVILION. 
 
 In the Eaviliou are exhibited : 
 
 1. The Collection of Meteorites (see the special guide), 
 
 2. Eocks (not yet arranged). 
 
 3. Speciinens too large for exhibition in the table-cases of 
 the Gallery, 
 
 4. A series of specimens arranged by Prof. John Ruskin to 
 illustrate some of the forms assumed by native silica. 
 
 Of the large specimens the following are worthy of special 
 notice : — 
 
 A fine specimen of Stibnite from Japan. • 
 A group of British and Indian minerals, arranged in the 
 centre of the long wall-case : including 
 
 Beautiful specimens of Apophyllite, Stilbite and Heulandite, 
 from the Syhadree Mountains : obtained during the construc- 
 tion of the Bombay and Poonah railroad, and presented in 
 1860 by Mr. J. J. Berkley. 
 
 ■A large specimen of crystallised Salt from the Punjaub, 
 presented in 1870 by Mr. R. Brandreth, 
 
 A large mass of ^rd from India. 
 
 Beautiful specimens of Calcite from Wheal Wrey and 
 Herodsfoot mine, Cornwall, and Wheal Friendship, Devon ; of 
 Fluor, from Weardale in Durham, and Menheniot and Herods- 
 foot mines, Cornwall ; of Harmotome from Strontian ; and 
 of Celestine from Pylle Hill, near Bristol : a specimen of 
 Barytes from Babbacombe, Devon, presented in 1837 by 
 Mr, G. Payne, 
 
 A table-top of Serpentine (Connemara marble) presented in 
 1826 by Mr. Richard Martin : resting on it is part of a large 
 nodule of iron, extracted by Professor Nordenskiold from the 
 basalt of Ovifak in 1870, and presented by him to the Trustees. 
 
 A table-top made of polished pebbles from Italian streams : 
 upon it is placed a specimen of albite-granite from San Piero 
 Elba, with many crystals of the pink variety of Tourmaline 
 still in their natural positions on the rock. 
 
The Pavilion. 115 
 
 On another table are placed 
 
 A polished specimen of Jasper Conglomerate from Kaimur, 
 Bandalkhand, India. 
 
 A large polished specimen of Derbyshire Fluor. 
 
 A large Agate, from Uruguay, cut in two and polished. 
 
 On a table ia the comer is an immense specimen of crys- 
 tallised Galena from the Great Laxey mine, Isle of Man. 
 
 Beneath the table is a large mammillary mass of Haematite, 
 from Lancashire. 
 
 In a special case are placed 
 
 1. A fine specimen of Selenite from lieinhardsbrunn : pre- 
 sented in 1847 by H.RH. tlie late Prince Consort. ■ 
 
 2. Two fine crystals of Iceland spar : one of them has been 
 cleaved to show the two images of a cross painted on the 
 opposite side of the specimen. 
 
 On a table in the next corner is an immense specimen of 
 green Jade from Battugol in Asiatic Kussia. 
 
 On another table is a fine specimen of crystallised Calcite 
 from Andreasberg. 
 
 On separate stands are placed several isolated crystals of 
 Quartz, remarkable for tTieir size, colour or tranparency; one of 
 them, a long doubly-terminated crystal, was presented in 1882 
 by C. S. Bement, Esq., of Philadelphia, U.S.A. 
 
 <^-<r-«.«SHJItS>'c)^>'3»J 
 
ALPHABETICAL INDEX 
 
 TO THE MINERALS MENTIONED IN THE GUIDE. 
 
 .Slschynite 
 
 Agate . 
 
 Alabandite 
 
 Alabaster 
 
 Albite . 
 
 Alexandrite 
 
 Allemontite 
 
 Ahnandine 
 
 Alum . 
 
 Alunite. 
 
 Amalgam 
 
 Amazon-stone 
 
 Amber . 
 
 Amethyst 
 
 Analcime 
 
 Anatase 
 
 Andalusite 
 
 Andrewsite 
 
 Anglesite 
 
 Anhydrite 
 
 Ankerite 
 
 Anorthite 
 
 Antimonite 
 
 Antimony. 
 
 Apatite. 
 
 Apophyllite 
 
 Aquamarine 
 
 Aragonite 
 
 Argentite 
 
 Arsenic. 
 
 Arsenolite 
 
 Asbestos 
 
 Astrophyllite 
 
 Atacamite 
 
 Augite . 
 
 Automolite 
 
 Avanturine 
 
 Axinite 
 
 CAOT 
 
 PAGE 
 
 34h 
 
 108 
 
 16b 
 
 94 
 
 4h 
 
 81 
 
 36h 
 
 109 
 
 29h 
 
 104 
 
 9e 
 
 89 
 
 2g 
 
 77 
 
 26f 
 
 102 
 
 37a 
 
 109 
 
 37a 
 
 109 
 
 2f 
 
 76 
 
 29a 
 
 104 
 
 42c 
 
 113 
 
 14g 
 
 93 
 
 29g 
 
 105 
 
 14a 
 
 92 
 
 26b 
 
 101 
 
 38g 
 
 111 
 
 36o 
 
 108 
 
 35b 
 
 108 
 
 20g 
 
 97 
 
 28g 
 
 104 
 
 6e 
 
 83 
 
 2g 
 
 77 
 
 40b 
 
 112 
 
 24f 
 
 100 
 
 30a 
 
 104 
 
 17a 
 
 96 
 
 3d 
 
 80 
 
 2g 
 
 76 
 
 15f 
 
 95 
 
 24c 
 
 99 
 
 28c 
 
 103 
 
 9d 
 
 87 
 
 21g 
 
 99 
 
 lOe 
 
 88 
 
 13e 
 
 93 
 
 33d 
 
 107 
 
 Babingtonito 
 
 Barytes 
 
 Barytocalcite 
 
 Bauxite 
 
 Beauxite 
 
 Beryl . 
 
 Biotite . 
 
 Bismuth 
 
 Bismuthite 
 
 Black copper 
 
 Blacklead 
 
 Blende. 
 
 Bloodstone 
 
 Boart . 
 
 Boracite 
 
 Borax . 
 
 Boumonite 
 
 Braunite 
 
 Brochantite 
 
 Bronzite 
 
 Brookite 
 
 Brudte. 
 
 Cacholong 
 
 Cairngorm 
 
 Calaite . 
 
 Calamine 
 
 Calcite . 
 
 Calcouranite 
 
 Caledonite 
 
 Calomel 
 
 Carbonado 
 
 Carbuncle 
 
 Camelian 
 
 Cassiterite 
 
 Cat's-eye 
 
 Celestine 
 
 . 24f 
 
 . 36a 
 
 . 21b 
 
 . 12f 
 
 . 12f 
 
 . 29c 
 
 . 28b 
 
 • 2g 
 
 . 6f 
 
 . 10c 
 
 . Ih 
 
 . 4b 
 
 . 16a 
 
 . If 
 
 . 37d 
 
 . 37o 
 
 . 7d 
 
 . 9f 
 
 . 35g 
 
 . 22h 
 
 . 14a 
 
 . lOd 
 
 . 15e 
 . 14f 
 . 38g 
 . 19h 
 . 18e 
 . 39c 
 . 37c 
 . 9b 
 . If 
 . 26f 
 . 16f 
 . llf 
 
 9e, 13f 
 
 . 35d 
 
 PAGE 
 100 
 
 108 
 
 97 
 
 91 
 
 91 
 
 104 
 
 103 
 
 77 
 
 83 
 
 88 
 
 79 
 
 80 
 
 94 
 
 78 
 
 110 
 
 110 
 
 84 
 
 89 
 
 109 
 
 99 
 
 92 
 
 88 
 
 95 
 93 
 
 111 
 97 
 96 
 
 112 
 
 110 
 86 
 78 
 
 101 
 
 95 
 
 91 
 
 I 89 
 
 I 93 
 
 108 
 
Index. 
 
 117 
 
 
 CASE 
 
 PAGE 
 
 
 OASE 
 
 PAOE 
 
 Cerargyrite . 
 
 . 8h 
 
 86 
 
 Dolomite 
 
 . 20d 
 
 97 
 
 Cerussite 
 
 . 18b 
 
 96 
 
 Dyscrasite 
 
 . 3a 
 
 80 
 
 Cervantite 
 
 . 15h 
 
 95 
 
 Dysluite 
 
 . lOe 
 
 88 
 
 Chabasite 
 
 . 31b 
 
 105 
 
 
 
 
 Chalcanthite . 
 
 . 35g 
 
 109 
 
 Edingtonile . 
 
 • 29g 
 
 105 
 
 Chalcedony . 
 
 . 15b 
 
 94 
 
 Eisenkiesel . 
 
 • 13g 
 
 93 
 
 Chalcophyllite 
 
 . 37h 
 
 111 
 
 Electrum 
 
 . 2e 
 
 75 
 
 Chalcopjrrite . 
 
 . 5b 
 
 84 
 
 Embolite 
 
 . 8h 
 
 86 
 
 Chalcotricliite 
 
 . 10c 
 
 88 
 
 Emerald 
 
 . 29c 
 
 104 
 
 Chalybite 
 
 . 20h 
 
 97 
 
 Emery. 
 
 . 9f 
 
 90 
 
 Chessylite 
 
 , 21d 
 
 98 
 
 Enstatite 
 
 . 22h 
 
 99 
 
 Childrenite . 
 
 . 40a 
 
 112 
 
 Epidote 
 
 . 27c 
 
 103 
 
 Chloanthite . 
 
 . 3c 
 
 80 
 
 Epsomitc 
 
 . 36h 
 
 109 
 
 Chlorargyrite. 
 
 . 8h 
 
 86 
 
 Erinite. 
 
 . 37h 
 
 111 
 
 Chlorites 
 
 32e-h 
 
 105 
 
 Erubescite 
 
 . 5e 
 
 84 
 
 Chromite 
 
 . lOg 
 
 89 
 
 Erythrite 
 
 . 38d 
 
 111 
 
 Chrysoberyl . 
 
 . 9e 
 
 89 
 
 Essonite 
 
 . 26e 
 
 102 
 
 ChrysocoUa . 
 
 . 25o 
 
 101 
 
 Euclase. 
 
 . 30b 
 
 104 
 
 Chrysolite . 
 
 . 22f 
 
 98 
 
 Eudialyte 
 
 . 34d 
 
 108 
 
 Chrysoprase . 
 
 . 16a 
 
 94 
 
 
 
 
 Churchite 
 
 . 38b 
 
 111 
 
 Felspar. 
 
 . 28g 
 
 103 
 
 Cinnabar 
 
 . 3h 
 
 81 
 
 Fergusonite . 
 
 . 34h 
 
 108 
 
 Cinnamon-Stoiio 
 
 . 26e 
 
 102 
 
 Fibrolite 
 
 . 26d 
 
 102 
 
 Clays . 
 
 . 30c 
 
 105 
 
 Fiorite . 
 
 . 15e 
 
 95 
 
 Clinochlore . 
 
 . 32f 
 
 106 
 
 Flint . 
 
 . 15b 
 
 94 
 
 Clinoolase 
 
 . 37h 
 
 111 
 
 Fluellite 
 
 . 9c 
 
 86 
 
 Coal , 
 
 . 41a 
 
 113 
 
 Fluor . 
 
 . 7e 
 
 86 
 
 Cobalt-Glance 
 
 • 6g 
 
 83 
 
 Franklinite . 
 
 . lOh 
 
 89 
 
 Cobaltine 
 
 . 6g 
 
 83 
 
 
 
 
 Columbite 
 
 . 34g 
 
 108 
 
 Gadolinite 
 
 . 22g 
 
 99 
 
 Connellite 
 
 . 37b 
 
 110 
 
 Galena . 
 
 . 4e 
 
 81 
 
 Copper. 
 
 . la 
 
 73 
 
 Garnet . 
 
 . 26e 
 
 102 
 
 Copper-Glance 
 
 . 3e 
 
 81 
 
 Glaiicodoie . 
 
 . 6h 
 
 83 
 
 Copper-Pyrites 
 
 . 5f 
 
 84 
 
 Gothite . 
 
 . 12a 
 
 90 
 
 Corundum 
 
 . 9f 
 
 89 
 
 Gold . 
 
 . 2b 
 
 74 
 
 Cotterite 
 
 . 14f 
 
 93 
 
 Graphite 
 
 . Ih 
 
 78 
 
 Crocidolite . 
 
 . 24a 
 
 99 
 
 Greenocldte . 
 
 . 5a 
 
 81 
 
 Crocoisite 
 
 . 35a 
 
 108 
 
 Grey Copper Ore 
 
 . 7a 
 
 84 
 
 Cromfordite . 
 
 . 22d 
 
 98 
 
 Gypsum 
 
 . 36f 
 
 108 
 
 Cronstedtite . 
 
 . 31e 
 
 106 
 
 
 
 
 Crookesite 
 
 . 5c 
 
 82 
 
 Hematite 
 
 . 11a 
 
 90 
 
 CryoUte. 
 
 . 9c 
 
 86 
 
 Haidingerite . 
 
 . 38b 
 
 110 
 
 Crystal. 
 
 . 14b 
 
 92 
 
 Halloysite 
 
 . 30c 
 
 105 
 
 Cuprite. 
 
 . 10a 
 
 87 
 
 Harmotome . 
 
 . 31d 
 
 105 
 
 Cuprouranite . 
 
 . 39d 
 
 112 
 
 Hauerite 
 
 . 5d 
 
 82 
 
 
 
 
 Hausmannite. 
 
 . lOh 
 
 89 
 
 Danaite. 
 
 . 6h 
 
 83 
 
 Haiiyne. 
 
 . 34b 
 
 107 
 
 Danalite 
 
 . 31h 
 
 106 
 
 Heavy Spar . 
 
 . 36a 
 
 108 
 
 Danburite 
 
 . 34a 
 
 107 
 
 Heliotrope 
 
 . 16a 
 
 94 
 
 Datholite 
 
 . 34a 
 
 107 
 
 Helvine 
 
 . 31h 
 
 106 
 
 Diamond 
 
 . If 
 
 78 
 
 Hemimorphite 
 
 . 25b 
 
 101 
 
 Diaspora 
 
 . 12b 
 
 91 
 
 Heulandite . 
 
 . 32c 
 
 105 
 
 Dichroite 
 
 . 28a 
 
 108 
 
 Hiddenite 
 
 . 23a 
 
 99 
 
 Dioptase 
 
 •. 22f 
 
 98 
 
 Hornblende . 
 
 . 23d 
 
 99 
 
118 
 
 Index. 
 
 Hornsilver 
 
 Hornstone 
 
 Humite. 
 
 Hyacinth 
 
 Hyalite 
 
 Hj-drophane 
 
 Hypersthene , 
 
 Iceland Spar 
 
 Idocrase 
 
 Ilmenite 
 
 Iridosmine 
 
 Iron 
 
 Iron-Pyrites 
 
 .Taoyntli 
 Jade . 
 Jadeite. 
 Jargoon. 
 Jasper . 
 Jordanite 
 
 Kaolinite 
 Kieserite 
 Kreittonite 
 Kyanite 
 
 Labradorite 
 
 Lanarkite 
 
 Langite. 
 
 Lapis Lazuli 
 
 Laumontite 
 
 Laurite. 
 
 Lazulite 
 
 Lead . 
 
 LeadhiUite 
 
 Lepidolite 
 
 Lepidomelane. 
 
 Lettsomite 
 
 Leucite . 
 
 Libethenite 
 
 Lievrite. 
 
 Limnite. 
 
 Limonite 
 
 Linarite. 
 
 Lirooonite 
 
 Ludlamite . 
 
 Ludwigite , 
 
 Lydian-Stone . 
 
 Magnesite 
 Magnetic Iron Ore 
 Magnetic Pyritc r 
 Magnetite 
 
 CASE 
 
 PAGE 
 
 8h 
 
 86 
 
 15a 
 
 94 
 
 22g 
 
 98 
 
 13b 
 
 92 
 
 16f 
 
 95 
 
 16g 
 
 95 
 
 221i 
 
 99 
 
 18e 
 
 96 
 
 25e 
 
 102 
 
 lid 
 
 90 
 
 2f 
 
 76 
 
 2f 
 
 75 
 
 5d 
 
 82 
 
 13b 
 
 92 
 
 24d 
 
 99 
 
 27a 
 
 102 
 
 13b 
 
 92 
 
 13g 
 
 93 
 
 8d 
 
 85 
 
 30b 
 
 105 
 
 36b 
 
 109 
 
 lOe 
 
 88 
 
 26c 
 
 101 
 
 28b 
 
 104 
 
 36f 
 
 108 
 
 35g 
 
 109 
 
 34b 
 
 107 
 
 29b 
 
 105 
 
 6d 
 
 83 
 
 39b 
 
 112 
 
 2f 
 
 75 
 
 37o 
 
 110 
 
 28e 
 
 103 
 
 28c 
 
 103 
 
 25h 
 
 109 
 
 28e 
 
 103 
 
 37e 
 
 111 
 
 27a 
 
 102 
 
 12f 
 
 91 
 
 12d 
 
 91 
 
 37b 
 
 109 
 
 40a 
 
 112 
 
 37g 
 
 HI 
 
 37o 
 
 110 
 
 15a 
 
 94 
 
 20d 
 
 97 
 
 lOf 
 
 88 
 
 6e 
 
 84 
 
 lOf 
 
 88 
 
 Malacbite 
 
 Manganite 
 
 . 12c 
 
 91 
 
 Marcasite 
 
 . 6b 
 
 82 
 
 Margarite 
 
 . 32h 
 
 106 
 
 Matlockite . 
 
 . 9c 
 
 87 
 
 Meerschaum . 
 
 . 23g 
 
 100 
 
 Melaconite . 
 
 . lOo 
 
 88 
 
 Melanterite. . 
 
 . 35e 
 
 109 
 
 Mendipite 
 
 . 9c 
 
 87 
 
 Mercury 
 
 .■ 2f 
 
 76 
 
 Mesitite 
 
 . 20h 
 
 97 
 
 Mesolite' 
 
 . 29e 
 
 105 
 
 Mica . 
 
 . 28a 
 
 103 
 
 Microcline 
 
 . 29a 
 
 104 
 
 Millerite 
 
 . 5b 
 
 81 
 
 Mimetesito . 
 
 . 40g 
 
 112 
 
 Mispickel 
 
 . 6h 
 
 83 
 
 Mocha Stone. 
 
 . 16e 
 
 94 
 
 Molybdenite . 
 
 . 6c 
 
 82 
 
 Muscovite 
 
 . 28d 
 
 103 
 
 Nagyagite . 
 
 . 5c 
 
 82 
 
 Natrolite 
 
 . 30g 
 
 105 
 
 Nepheline 
 
 . 28f 
 
 103 
 
 Nephrite 
 
 . 24d 
 
 99 
 
 Nickel-Glance 
 
 • 6g 
 
 83 
 
 Nickeline 
 
 . 3a 
 
 80 
 
 Nitratine 
 
 . 37d 
 
 110 
 
 Nitre . 
 
 . 37d 
 
 110 
 
 Oligoclase 
 
 . 27e 
 
 104 
 
 Olivenite 
 
 . 37e 
 
 111 
 
 Olivine . 
 
 . 22f 
 
 98 
 
 Onyx . 
 
 . 16c 
 
 94 
 
 Opal . 
 
 . 16f 
 
 95 
 
 Orangite 
 
 . 13c 
 
 92 
 
 Orpiment 
 
 ■ 6g 
 
 83 
 
 Orthoclase 
 
 . 27e 
 
 104 
 
 Osteolite 
 
 . 40d 
 
 112 
 
 Parisite. 
 
 . 22d 
 
 98 
 
 Pennine. 
 
 . 32e 
 
 105 
 
 Pentlandite . 
 
 . 4h 
 
 81 
 
 Periclase 
 
 . 10c 
 
 88 
 
 Pericline 
 
 . 29b 
 
 104 
 
 Peridot . 
 
 . 22f 
 
 98 
 
 Perofskite 
 
 . 34o 
 
 108 
 
 Pharmacolite. 
 
 . 38b 
 
 110 
 
 Pharmacosiderite 
 
 . 38d 
 
 111 
 
 Phenakite 
 
 . 22e 
 
 98 
 
 Phlogopite . 
 
 . 28a 
 
 103 
 
 Phosgenite . 
 
 . 22d 
 
 98 
 
 Phosphorite . 
 
 . 40d 
 
 112 
 
 Pitchblende . 
 
 . lOh 
 
 89 
 
 CASE 
 
 22b 
 
Index. 
 
 X19 
 
 Plasma. 
 
 Platiuum 
 
 Pleonasto 
 
 Plumbago 
 
 Pollucite 
 
 Povpezite 
 
 Potato Stone , 
 
 Prase . 
 
 Prehnite 
 
 Proustite 
 
 Psilomelane 
 
 Pyrargyrite 
 
 Pyrites . 
 
 Pyrolusite 
 
 Pyromorphite 
 
 Pyrope . 
 
 Pyrophyllite 
 
 Pyrosmalite 
 
 Pyrrliite 
 
 Pyrrhotine 
 
 Quartz . 
 Quicksilver 
 
 Eealgar. 
 Kedruthite 
 Ehabdophane 
 Ehodicite 
 Bhodoohrosite 
 Rhodonite 
 Eipidolite 
 Rook Crystal 
 Rubellite 
 Ruby . 
 Ruby Copper , 
 EutUe . 
 
 Sal-Ammoniac 
 
 Salt . 
 
 Saltpetre 
 
 Samarskite 
 
 Sapphire 
 
 Sapphire d'eau 
 
 Sarcolite 
 
 Sard . 
 
 Sardonyx 
 
 Sassoline 
 
 Soapolite 
 
 Scheelite 
 
 Scoleoite 
 
 Soorodite 
 
 Scovillite 
 
 Selenite 
 
 Senarmontite , 
 
 CASE 
 
 16a 
 
 2f 
 lOf 
 
 Ih 
 29h 
 
 2c 
 14e 
 13e 
 30e 
 
 8b 
 12f 
 
 8a 
 
 5d 
 lie 
 40e 
 26h 
 30d 
 31h 
 34h 
 
 5e 
 
 14b 
 
 2f 
 
 6o 
 , 3e 
 38b 
 . 37c 
 . 19h 
 . 24e 
 , 32h 
 . 14b 
 . 33a 
 . 9h 
 . 10a 
 . 13d 
 
 PAGE 
 
 94 
 
 75 
 
 88 
 
 79 
 
 105 
 
 75 
 
 93 
 
 93 
 
 105 
 
 84 
 
 91 
 
 84 
 
 82 
 
 91 
 
 112 
 
 102 
 
 105 
 
 106 
 
 108 
 
 84 
 
 92 
 76 
 
 83 
 
 81 
 
 111 
 
 110 
 
 97 
 
 100 
 
 106 
 
 92 
 
 107 
 
 90 
 
 87 
 
 92 
 
 8f 
 37d 
 34g 
 
 9h 
 28a 
 25g 
 16a 
 16b 
 15g 
 25g 
 33g 
 
 29f 
 38e 
 38b 
 36g 
 
 15f 
 
 85 
 
 110 
 
 108 
 
 90 
 
 103 
 
 102 
 
 94 
 
 94 
 
 95 
 
 102 
 
 108 
 
 105 
 
 111 
 
 111 
 
 108 
 
 95 
 
 Serpentine 
 
 Silver . 
 
 Skutterudito 
 
 Smaltine 
 
 Soapstone 
 
 Soda Nitre 
 
 Sodalite 
 
 Sombrerite 
 
 Spathic Iron 
 
 Spartalite 
 
 Specular Iron 
 
 Sphene . 
 
 Spinel . 
 
 Spodumene 
 
 Star-Stone 
 
 Staurolite 
 
 Steatite . 
 
 Stephanite 
 
 Stibnite 
 
 Stilbite. 
 
 Stolzite. 
 
 Stream Tin 
 
 Strontianite 
 
 Sulphur 
 
 Susannite 
 
 Sylvanite 
 
 Sylvine. 
 
 Talc . 
 
 TeUurium 
 
 Tennantite 
 
 Tephroite 
 
 Tetrahedrite 
 
 Thorite. 
 
 Tile Ore 
 
 Tin 
 
 Tin Stone 
 
 Topaz . 
 
 Touchstone 
 
 Tourmaline 
 
 Tridymite 
 
 Tscheffkinite 
 
 Turgite. 
 
 Turquoise 
 
 Ullmannite 
 
 Uranocircite 
 
 Uwarowite 
 
 Valentinite 
 Vanadinite 
 Vermiculite 
 Vivianite 
 
 OASE 
 
 FACE 
 
 25a 
 
 101 
 
 Ic 
 
 74 
 
 3o 
 
 80 
 
 3b 
 
 80 
 
 23g 
 
 100 
 
 37d 
 
 110 
 
 31h 
 
 106 
 
 40d 
 
 112 
 
 20h 
 
 97 
 
 10c 
 
 88 
 
 lib 
 
 90 
 
 34d 
 
 108 
 
 lOe 
 
 88 
 
 23a 
 
 99 
 
 9h 
 
 90 
 
 26o 
 
 101 
 
 23g 
 
 100 
 
 5h 
 
 84 
 
 6e 
 
 83 
 
 32a 
 
 105 
 
 33g 
 
 108 
 
 13a 
 
 92 
 
 18b 
 
 96 
 
 le 
 
 77 
 
 37c 
 
 110 
 
 6d 
 
 83 
 
 8f 
 
 85 
 
 23g 
 
 100 
 
 2h 
 
 76 
 
 7b 
 
 84 
 
 22f 
 
 98 
 
 7a 
 
 84 
 
 13c 
 
 92 
 
 10b 
 
 88 
 
 2f 
 
 75 
 
 llf 
 
 91 
 
 25c 
 
 101 
 
 15a 
 
 94 
 
 33a 
 
 106 
 
 lib 
 
 92 
 
 34f 
 
 108 
 
 12d 
 
 91 
 
 38g 
 
 111 
 
 6g 
 
 83 
 
 39c 
 
 112 
 
 26h 
 
 102 
 
 15g 
 
 95 
 
 29e 
 
 112 
 
 32e 
 
 106 
 
 38o 
 
 111 
 
120 
 
 Index. 
 
 Wad . 
 
 Wagnerite 
 
 Waringtonite 
 
 Wavellite 
 
 Whewellite 
 
 Willemite 
 
 Witherite 
 
 Wolfram 
 
 Wollastonite 
 
 CASE 
 
 PAOE 
 
 12h 
 
 91 
 
 39e 
 
 112 
 
 35g 
 
 109 
 
 38f 
 
 111 
 
 391i 
 
 112 
 
 22e 
 
 98 
 
 18a 
 
 96 
 
 331i 
 
 108 
 
 24e 
 
 100 
 
 Wood Tin . 
 
 Wulfenite 
 
 Wurtzite 
 
 Xanthoconite. 
 
 Zeolites 
 Zincite. 
 Zircon . 
 
 CASE 
 
 13a 
 33e 
 
 30©-32d 
 , lOo 
 . 13b 
 
 FASE 
 
 91 
 
 108 
 
 81 
 
 85 
 
 105 
 88 
 92 
 
 LONDON : FBIKTKD B7 WUiLIAU CLOWES AND bUNS, UMITKD, STAUf OfiD 8IUEEX 
 AHD CiTAUIHG CItOES.