EARTH 
 
 sen NCES 
 
 UMJARY LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 GIFT 
 
 Received 
 Accession No. 
 
 *jooy 
 
 , i8g 
 . bass No. 
 

 22, 
 
UIITBRSITT 
 
 THE DIAMOND 
 
CL 
 
PAPERS AND NOTES 
 
 ON THE 
 
 GENESIS AND MATRIX 
 
 OF 
 
 THE DIAMOND 
 
 BY THE LATE 
 
 HENRY CARVILL LEWIS, M.A., F.G.S. 
 
 \v 
 
 PROFESSOR OP MINERALOGY IN THE ACADEMY OF NATURAL SCIENCES, PHILADELPHIA 
 PROFESSOR OF GEOLOGY IN HAVERFORD COLLEGE, U.S.A. 
 
 EDITED FROM HIS 'UNPUBLISHED MSS. 
 
 BY 
 
 PROFESSOR T. G. BONNEY 
 
 D.Sc., LL.D., F.E.S., &c. 
 
 LONGMANS, GREEN, AND CO. 
 
 39 PATERNOSTER ROW, LONDON 
 NEW YORK AND BOMBAY 
 
 1897 
 
 [All rights reserved] 
 
\o 
 
 EARTH 
 SCIENCES 
 
 LIBRARY 
 
x 
 
 NOTE 
 
 MRS. CABVILL LEWIS gladly avails herself of this oppor- 
 tunity to express her indebtedness and gratitude to Professor 
 T. G. BONNEY for his kindness in arranging and editing 
 the papers and notes contained in this book, in accordance 
 with the wishes of the late Professor Henry Carvill Lewis, 
 whose desire it was that his researches on the origin and 
 matrix of the diamond should be given to the scientific 
 world. 
 
PREFACE 
 
 A FEW words of explanation are necessary in order to 
 indicate my connection with this book and what has or 
 has not been attempted in preparing it for publication. 
 Shortly after the death of Professor Carvill Lewis in July 
 1888, in accordance with directions given during his last 
 illness, the manuscripts of his two papers on the diamond- 
 bearing rocks of Kimberley, communicated to the British 
 Association at the meetings in 1886 and 1887 respectively, 
 together with the specimens on which he had worked and 
 a number of miscellaneous notes, were given by Mrs, 
 Lewis to Professor G. H. Williams of the Johns-Hopkins 
 University, who had kindly promised to carry out his late 
 friend's desires by preparing the incomplete material for 
 publication, as soon as his other duties and engagements 
 permitted. But the pressure of these was so great that an 
 opportunity had not been found when he too was taken 
 away from this world by the same disease (typhoid fever) 
 which had proved fatal to Professor Lewis. As I have 
 been for many years a student of the structure and history 
 of olivine rocks and serpentines, I had felt great interest in 
 the papers to which I had listened at Birmingham and 
 Manchester, and thought it would be most unfortunate if 
 the numerous careful and minute observations which they 
 
viii PREFACE 
 
 contained were much longer delayed in publication, or, 
 perhaps, were even lost to science. Accordingly I informed 
 Mrs. Lewis that if she would entrust the manuscripts to 
 me I would do my best to arrange them for publication, 
 stating at the same time that I could not attempt more 
 than to act as an editor to the materials which had 
 been left by her late husband. From some of the docu- 
 ments it was obviously his intention, had his life been 
 spared, to have carried on his researches and to have made 
 additions to the original papers so as to bring the subject 
 down to the date of publication. But this task, as I told 
 Mrs. Lewis, I could not undertake. Parts of the subject 
 lay rather ou f side my usual lines of work, so that very 
 much time would have had to be spent in hunting through 
 the geological, and more especially mineralogical, literature 
 of the last eight or nine years on the chance of finding 
 something throwing light on the questions treated by 
 Professor Lewis. As the hours which I can devote to 
 prosecuting my own investigations are none too numerous 
 already, I was unable to undertake what would have been 
 of little profit and hardly any interest. To me no work is 
 so irksome as that of searching through periodicals on 
 the chance of lighting upon some contribution -possibly 
 in itself of little value to the literature of a subject. 
 
 Thus the two papers, forming the first and second 
 sections of this book, are printed very nearly as they were 
 left by Professor Lewis. The references have been tested 
 and corrected, and a few changes have been made here 
 and there in phrase or in the order of sentences. These 
 changes, however, are merely editorial, such as the author 
 himself would have most probably made in finally revising 
 his manuscript for the press. Accordingly the statements 
 printed and the results given represent his views, at 
 
PREFACE ix 
 
 any rate in 1887, and, so far as I know, at the time of his 
 death. Of the third section nothing had been written ; the 
 materials consisted only of some very brief 'jottings ' and 
 a small set of rock specimens. The latter, however, 
 appeared to me to have such an important bearing on the 
 subject of the first two sections that I have drawn up a 
 statement of the facts concerning them from such literature 
 as I have found, and have written some brief descriptions 
 of the structures, macroscopic and microscopic, of the 
 specimens themselves. 
 
 In addition to the above-named materials, Professor 
 Lewis left numerous notes on the occurrence of diamonds 
 in other countries, and on various matters bearing more or 
 less indirectly on the subject of the two papers. Two 
 pocket-books also were placed in my hands, containing 
 memoranda of a journey through some districts in the 
 United States where diamonds had been, or were said to 
 have been, discovered. From these I compiled two other 
 sections, weaving the materials of the latter, after con- 
 siderable condensation, into a continuous narrative. 
 The manuscript was set up in type, but Professor Kosen- 
 busch, to whom the whole of the proofs were submitted, 
 was of opinion that they would not augment the value of 
 the earlier part of the book, because the notes on localities 
 were obviously incomplete, and the journeys were more 
 negative than positive in their results. Moreover, many of 
 the facts recorded had already, owing to the lapse of time, 
 become incorporated into literature readily accessible to 
 students. I had myself felt a like misgiving, but, for a 
 reason which will appear below, felt bound to alter or to 
 cancel as little as possible. But when fortified by such 
 an authority on this special topic as Professor Eosenbusch, 
 in whose laboratory at Heidelberg much of the work 
 
x PREFACE 
 
 embodied in the first and second section had been done, I 
 had no hesitation (with the concurrence of Mrs. Lewis) in 
 following his advice. So this portion has been cancelled, 
 and as the book now stands it comprises all the manuscript 
 that Professor Lewis had left in a fairly complete state, with 
 a little supplementary work which has a very direct bearing 
 on the subject of his two papers, and for which he had 
 coljected specimens. 
 
 Several months elapsed, owing to various circum- 
 stances, before Mrs. Lewis could place the late Professor's 
 manuscripts and the other materials in my hands. In the 
 interval Sir J. B. Stone, M,P., when I was a guest at 
 Erdington Grange, his pleasant home near Sutton Gold- 
 field, showed me a collection of specimens which he had 
 obtained during a recent visit to the Kimberley mines. 
 Among these were two lumps of the diamond-bearing rock, 
 each as large as three or four ordinary cabinet specimens, 
 and in a much better state of preservation than any which 
 I had previously seen. One of these he kindly gave to me, 
 asking me to examine its structure, and allowing me to 
 make use of ttye other materials in his possession. Some 
 microscopic sections were prepared from this specimen, 
 and, in addition to others already in my collection, the gift 
 of Professor Boyd Dawkins, I had the advantage of studying 
 one or two small but well-preserved pieces of the rock, which 
 had been presented to Miss C. A. Raisin by C. J. Alford, Esq., 
 as well as others kindly lent to me by the late Professor 
 A. H. Green. 1 The results of these studies were published 
 in the Geological Magazine for 1895 (pp. 492-502) in a 
 paper jointly written by Sir J. B. Stone, Miss C. A. Raisin, 
 
 1 He died after a short illness, the result, I fear, of overwork, in August 
 1896. A good geologist and a most unselfish man, multis ille bonis flebilin 
 occidit ! 
 
PREFACE xi 
 
 and myself. Our conclusions in one respect differed a little 
 from those expressed by my lamented friend Professor 
 Lewis viz. as to the origin of the diamond -bearing rock 
 to which he has given the name Kimberlite. Its precise 
 nature is undoubtedly very difficult to determine. It 
 differs from any rock, whether peridotite or serpentine, 
 known to me, and my experience, especially in regard to 
 the latter, is a rather large one. Its structure is hardly 
 such as I should expect to result from the hydration of a 
 glass, the chemical composition of which nearly corre- 
 sponded with that of olivine, and it seems to me improbable 
 that the material would have remained in a glassy con- 
 dition throughout pipes or necks of such great size, which, 
 also have now been excavated to a considerable depth. 
 Olivine is not a very fusible mineral, and vitreous peridotites 
 are even more rare and limited in extent than tachylites ; 
 indeed, I am doubtful whether I have ever really met 
 with one. Some, indeed, of the fragments in these 
 diamond-bearing breccias (for, whatever may be the ex- 
 planation, they undoubtedly exhibit a brecciated structure) 
 may probably do represent either a glassy or at any 
 rate a very compact form of peridotite (now converted into 
 serpentine) ; but I regard them, together with the olivine, 
 augite, mica, garnets, and other large minerals (not ex- 
 cluding the diamonds) as true ' fragments,' like the pieces 
 of shale which are sometimes found associated with them, 
 produced by the explosive destruction of more coarsely 
 crystalline rocks of earlier consolidation, and not the result 
 of a fluxional movement in a magma which had previously 
 reached a stage of partial separation and incomplete con- 
 solidation, and had in addition incorporated fragments of 
 overlying rocks in its upward progress. The subject, how- 
 ever, is one of great difficulty, and it may be that Professor 
 
xii PREFACE 
 
 Lewis' explanation is the more correct one. I refer to my 
 own conclusions only because they were formed quite inde- 
 pendently ; for at that time abstracts merely of Professor 
 Lewis' papers had been published, and from these I had 
 formed the impression that the name ' kimberlite ' designated 
 the serpentinous fragments which were embedded in the 
 breccia, and not the rock itself. But whatever be the 
 ultimate result of that part of the inquiry, this would not 
 necessarily affect my friend's views as to the genesis of 
 the diamond viz. by the action of an extremely basic rock 
 upon carbonaceous material or diminish the value of his 
 elaborate researches into the structure and mineral com- 
 position of its matrix. 
 
 There remains only the pleasant duty of returning, on 
 behalf of Mrs. Lewis and for myself, most hearty thanks 
 to two friends : to J. J. H. Teall, Esq., F.E.S., who has 
 most kindly taken the admirable micro-photographs of the 
 slices of the Kimberley and the Kentucky rock, in order to 
 illustrate this work ; and to Professor Kosenbusch, who has 
 been so good as to read and criticise the proofs. Only 
 those who, like the editor, have learned from experience of 
 his books the rich stores of his mineralogical and petro- 
 graphical knowledge can fully appreciate the value of his 
 generous assistance in putting on record some of the 
 work produced by one who studied in his laboratory at 
 Heidelberg. 
 
 T. G. BONNEY. 
 
CONTENTS 
 
 5ECTION 
 
 I. PAPER READ IN 1886 . 
 
 II. PAPER READ IN 1887 ..;... 10 
 
 III. KIMBERLITE FROM THE UNITED STATES 
 
 NOTE . . . . . , . . . 68 
 
 INDEX 70 
 
LIST OF ILLUSTRATIONS 
 
 PLATES 
 PLATE I 
 
 FRAGMENT OP THE DIAMOND -BEARING BOCK PROM KIMBER.LEY 
 (NATURAL SIZE) . . ' . . , . r> , Frontispiece 
 
 This specimen was obtained at the diamond workings by Sir J. B. Stone, 
 M.P., F.G.S., in 1894, and given by him to the editor. It cam from the De 
 Beers mine, and from the deepest level then worked viz. rather more 
 than 1,000 feet. It is a characteristic but slightly coarse variety of the 
 rock, in very good preservation, exhibiting very well its peculiar brecciated 
 structure. The largest fragment is a rather decomposed compact serpen- 
 tinous rock ; the smaller grains are mostly mineral partially serpentinised 
 olivines and pyroxenes, with a few flakes of mica, which, however, cannot 
 be distinguished in the plate, 
 
 PLATE II 
 
 MICROSCOPIC STRUCTURE OP PART OF A SLICE CUT PROM THE 
 SPECIMEN OF KIMBERLEY EOCK REPRESENTED IN PLATE I. 
 (x 22 DIAMETERS) , / (Upper Figure] , To face p. 72 
 
 Nearly in the centre of the figure is a rather rounded grain of mica, showing 
 the Usual cleavage, and bordered by alteration products (p. 25). The 
 large grain, part of which is shown on the S.W. side, is moat probably 
 enstatite, serpentinised externally, the difference of tint in the border 
 corresponding with a slight difference in the character of the replacinig 
 mineral. The smaller grain near the mica (to the S.E.) probably is 
 also enstatite, but completely changed 5 others are serpentinised olivine, 
 but larger grains of this mineral, only changed at the border, occur in 
 other parts of the slice. The grain partly included in the figure and 
 to the W.N.W. of the mica is very compact in structure, seemingly 
 composed of minute serpentinous materials, and possibly may be a rock 
 fragment (? of a glassy peridotite). The separate mineral grains, as will be 
 seen, decrease in size till they become indistinguishable from the granular 
 matrix of serpentine, calcite or dolomite, iron oxide, perovskite, &c. 
 
xvi LIST OF ILLUSTRATIONS 
 
 PLATE II 
 
 MICROSCOPIC STRUCTURE OF PART OF A SLICE CUT FROM A SPECIMEN 
 OF KlMBERLITE FROM ELLIOTT COUNTY, KENTUCKY ( x 28 DlA- 
 METERS) ; see PAGE 66 . . (Lower Figure) . To face p. 72 
 
 To the S.S.E. of the centre and rather nearer to the edge is a grain of biotite, 
 showing cleavage planes, and slightly bordered as above. The large grain, 
 partly included to the S.S.W., is olivine, almost wholly converted to 
 serpentine. The remaining grains are the same mineral in various stages 
 of change, but the rather large one just N. of the centre possibly may bo 
 enstatite. The matrix consists, as before, of a mixture of granules of 
 serpentine, iron oxide, perovskite, fcc. 
 
 ILLUSTRATIONS IN TEXT 
 
 FIG. PAGE 
 
 1. Du TOIT'S PAN MINE, 1885 . . . , . . . . .j . 3 
 
 2. DE BEERS MINE, 1885 . . . . . ... . . 8 
 
 3. OLIVINE CRYSTAL SEEN PARALLEL TO ocPcc 13 
 
 4. 5. CORROSION CAVITIES . 13 
 
 6. TREMOLITE . . . . . . . .'..; 15 
 
 7. Two OLIVINE CRYSTALS . . . . -. , y .'.-,'. .' ..^" . 15 
 8-10. ALTERATIONS or OLIVINE . . . . .~ . ..- , .16 
 
 11-13. EUTILE IN OLIVINE . . . . . , .- ... 16 
 
 14. KUTILE . . ' . . 17 
 
 15, 16. BUTILE WITH TITANIC IRON . . 17 
 
 17. OLTVTNE AND DIOPSIDE FROM KENTUCKY PERIDOTITE . . ." . 17 
 
 18. ENSTATITE AND BIOTITE .... 17 
 
 19. PEROVSKITE . . . . . '. '. . . . .29 
 20-23. TWINNED PEROVSKITE . . . . - 30 
 
 24. TWINNED PEROVSKITE * . .31 
 
 25. TWINNED PEROVSKITE 32 
 
 26. INCLUSIONS IN PEROVSKITE 33 
 
 27. TITANIC IRON IN PEROVSKITE .... . ;. , / . 33 
 28,29. PEROVSKITE SURROUNDING OLIVINE ...... ._ .,.._. 34 
 
 30. PEROVSKITE . . . - .*- . * : y --....-* r5^ . 36 
 
 31. CYANITE. ... .^ . ^ , . . .. . f - .... .39 
 
 32. MINUTE DIAMONDS . . . ... ... v _ . 41 
 
 33. MICROSCOPIC SECTION OF KIMBERLEY PERIDOTITE . . . .. .42 
 
 34. SHALE FRAGMENT FILLED WITH THE GROUND-MASS ... . . . 46 
 
 35. SHALE FRAGMENT SURROUNDED BY CALCITE . . . . .46 
 

 
 SECTION I 
 
 ON A DIAMOND-BEARING PEEIDOTITE AND ON 
 THE HISTORY OF THE DIAMOND 
 
 BY H. CARVILL LEWIS, M.A., F.G.S. 
 
 (Read at the Meeting of the British Association at Birmingham, 1886 ') 
 
 THE discovery of diamonds at Kimberley, South Africa, has 
 proved to be a matter not only of commercial but also of much 
 geological interest. Here the diamonds occur under con- 
 ditions which are unlike those of any other known locality, 
 and are worthy of special attention. 
 
 The first diamond was found in South Africa in 1867, 
 when a large specimen was picked out of a lot of rolled 
 pebbles gathered in the Orange Eiver. This led to the 
 river diggings in the Orange and Vaal rivers, which con- 
 tinue to the present time, but are now only worked at three 
 or four points. 
 
 In 1870, when perhaps 10,000 persons had gathered 
 along the banks of the Vaal River, the news came of the dis- 
 covery of diamonds at a point some 15 miles away from the 
 river where the town of Kimberley now stands. These were 
 the* so-called ' dry diggings,' which at first were thought to 
 be alluvial deposits, but have proved to be volcanic pipes 
 of a highly interesting character. In 1871 four mines 
 were discovered in close proximity to Kimberley, all of 
 "which have since become famous. They are known as Du 
 Toits Pan, De Beers, Kimberley, and Bulfontein mines, all 
 
 1 This date must be understood as limiting the phrases applying to time 
 throughout the paper. 
 
 B 
 
2 ON A DIAMOND-BEAEING PEEIDOTITE AND 
 
 of which could be enclosed by a circle 3J miles in diameter. 
 The mines lie at the northern end of a great plateau, 
 known as the Upper Karoo Plateau, which extends from 
 the Bokkevelft mountains at the Cape of Good Hope to the 
 border of tW Transvaal Kepublic, varying in elevation 
 from 2,700 to 6,000 feet above sea level. 1 The four princi- 
 pal mines at Kimberley, at an elevation of about 3,900 
 feet, are close to one another. The two principal mines in 
 the Orange Free State (Koffee-fontein and Jagers-fontein) 
 lie S.E. of Kimberley, the former 30 miles, the latter 60 
 miles distant. 
 
 In 1872, 30,000 persons had assembled about the four 
 mines, and other mines were soon discovered in the neigh- 
 bouring territory. At the present time, 15 distinct diamond 
 mines (dry diggings) are known in Griqua Land, Urot and 
 the adjoining Orange Free State ; none of the others, how- 
 ever, as yet equal in richness the four great mines first 
 discovered. These four all have the same geological 
 structure, each being a separate pipe ; and all are re- 
 markably rich in diamonds. It has been estimated that 
 since the opening of these mines more than six tons of 
 diamonds 2 have been extracted from them, being probably 
 greater than the total combined previous production of all 
 the other mines in the world. It was soon discovered that 
 these pipes went down vertically to an unknown depth, 
 penetrating the surrounding strata. 
 
 The diamond-bearing material first excavated was a 
 soft yellowish friable substance, readily crumbling when 
 exposed. At the depth of about 100 feet it became darker 
 and harder, and finally acquired a slate blue or dark green 
 colour, resembling some varieties of serpentine. This is 
 the well-known ' blue earth ' of the diamond mines, which 
 proved to be richer in diamonds than the wholly decom- 
 
 1 Cape of Good Hope Official Handbook, 1886, p. 169. 
 
 2 T. Reunert, Cape of Good Hope Official Handbook, 1886, p. 212. 
 Moulle, ' Memoire sur la geologic generale et sur les mines de diamants 
 de 1'Afrique du Sud,' Ann. des Mines, vii. 1885, p. 193. 
 
ON THE HISTORY OF THE DIAMOND 3 
 
 posed and weathered portion first penetrated, and called 
 ' yellow ground.' This * blue earth ' or ' blue ground ' is 
 taken out of the mine and exposed to the sun, and it is 
 then capable of being readily crushed and washed for the 
 extraction of its included diamonds. The ' blue ground ' 
 is greasy to the touch like serpentine, and is full of enclosed 
 fragments of slate and other substances. It has been found 
 to become harder and more stony the deeper it is pene- 
 trated, and to continue vertically downwards to an un- 
 known depth. The deepest sinkings in Kimberley mine 
 are now 600 feet below the surface, still in the same 
 compact material. 1 At this depth the true nature of the 
 diamond-bearing substance is more clearly apparent than 
 
 FIG. 1. Du Toit's Pan Mine, 1885. (Sketch by Professor Lewis from the Colonial Exhibition, 
 1, debris ; 2, yellow shale ; 3, black shale ; 4, diamond-bearing rock 
 
 it was when the workings were carried on in the more de- 
 composed material. Quite recently, both in the Kimberley 
 and De Beers mines the remarkable rock has been reached 
 which forms the subject of the present paper. 
 
 The first scientific publication regarding the matrix of 
 the Kimberley diamonds appears to be that of Prof. E. Cohen, 
 in 1872, 2 and, in England, of Mr. E. J. Dunn, in 1873. 3 
 Before that date, however, Mr. G. W. Stow 4 and Dr. John 
 Shaw 5 had described the general geology of the region, and 
 
 1 They have been carried to a very much greater depth since 1886. 
 T. G. B. ' 2 Neues Jahrb. 1872, p. 857. 
 
 3 Quart. Journ. Geol. Soc. xxx. 1874, p. 54. 
 
 4 Ibid, xxviii. 1872, p. B (cf. Geol. Mag. 1871, p. 49). 5 Ibid. p. 21. 
 
 u 2 
 
4 ON A DIAMOND-BEARING PERIDOTITE AND 
 
 Prof. T. Eupert Jones and Mr. Thos. Davies had identified 
 a number of the minerals occurring associated with the dia- 
 mond. Mr. Dunn has described the occurrence so well- that 
 I cannot do better than quote some extracts from his paper. 1 
 ' The conditions under which diamonds occur in South 
 Africa are quite different from those of every other known 
 locality, and are so unusual as to deserve the earnest 
 attention of all geologists. 
 
 * At the junction, and back for a distance of from one 
 to several feet, the edges of the shale are bent sharply 
 upwards. The contents of these "pipes" in the shale are 
 the same in all cases, and show distinctly that they are of 
 igneous origin. The base is more or less decomposed 
 gabbro (?) or euphotide (?), through which are scattered 
 particles, fragments, and huge masses of shale, nodules 
 of doleri.te, occasional fragments of chloritic schist, 
 micaceous schist and gneiss. The principal foreign in- 
 gredient is the shale, which in many places, particularly 
 at Colesberg Kopje, is thoroughly comminuted, forming a 
 breccia with euphotide (?) as a base. Where large masses of 
 shale occur, the lines of the bedding, as might be expected, 
 are not horizontal, but lie in all directions. 
 
 * For a depth of from 30 to 40 feet, cracks, joints, and 
 irregular cavities filled with red sand from the surface 
 penetrate ; with the sand, and showing that it has come 
 from the surface, are fragments of ostrich egg-shell, small 
 rounded grains of chalcedony, agate, &c., identical with the 
 same substances mixed with the surface soil. 
 
 'At 130 feet, the greatest depth so far attained, the 
 rock becomes compact, tough, and shows the original 
 texture, though the ingredients are altered, notably the 
 pyroxene or augite into bronzite. 2 
 
 ' The entangled blocks of shale and sandstone are fre- 
 quently altered, the latter sometimes into quartz rock. 
 
 1 Quart. Journ. Geol. Soc., xxx. 1874, p. 54. 
 
 2 Probably diallage is here meant; the name bronzite, which formerly 
 was used somewhat vaguely, being now restricted to a rhombic pyroxene. 
 T. G. B. 
 
ON THE HISTORY OF THE DIAMOND 5 
 
 ' A very well-known fact on the diamond-fields, and one 
 rather in favour of the euphotide (?) being the mother rock, 
 is that each of the pipes furnishes diamonds easily distin- 
 guishable from those found in the others. Bulfontein pro- 
 duces small white stones, occasionally specked and flawed, 
 but very rarely coloured ; while Du Toits Pan, within half 
 a mile, seldom yields other than coloured stones. So well 
 marked are the characteristics of the diamonds from the 
 various diggings, that diamond buyers can generally tell by 
 the appearance of a stone the locality from which it has come.' 
 
 Mr. Dunn's paper was followed in the same year by a de- 
 scription of the microscopic character of the diamond-bearing 
 rock by Professor N. S. Maskelyne and Dr. W. Flight. 1 
 
 The specimens examined and analysed by them were 
 unfortunately all decomposed more or less, none coming 
 from a depth greater than 180 feet. They identify a 
 bronzite (two varieties, one bright green, one buff coloured), 
 a variety of smaragdite, garnet, ilmenite, a diallage (much 
 altered) and a mica-like mineral. Opaline silica, occasion- 
 ally hyalite, sometimes resembling hornstone, is dissemi- 
 nated through the rock ; the mica-like mineral is described, 
 analysed, and named vaalite, it being regarded as an out- 
 lying member of the vermiculite family ; the smaragdite, 
 in brilliant greyish green fragments, green bronzite and a 
 much altered bronzite, resembling that in the meteorite of 
 Breitenbach, are also analysed, as is the rock of Bulfontein. 
 This gives (water being undetermined) : 
 
 CaC0 3 . . . 
 
 . 59-625 
 
 M g co 3 . . : 
 
 . 4-972 
 
 FeC0 3 . 
 
 3-016 
 
 Si0 2 
 
 . 20-700 
 
 A1 2 3 
 
 0-553 
 
 FeO . . . 
 
 < . 4-296 
 
 MgO . . . 
 
 ,_ . 5-799 
 
 CaO 
 
 0-524 
 
 
 99*485 
 
 Quart. Joimi. Gcol. Soc. xxx. 1874, p. 406. 
 
6 ON A DIAMOND-BEARING PEEIDOTITE AND 
 
 Additional particulars, of which a brief summary is 
 subjoined, are supplied in more recent papers by Mr. 
 Dunn, 1 which are founded upon facts brought to light 
 by fresh excavations. 
 
 The bedding of the black shales surrounding the mines 
 is turned upwards at the edges of the pipe. These shales 
 are very combustible and carbonaceous ; in one part of 
 Kimberley Mine, where accidentally fired, they have 
 smouldered on for eighteen months. The shales extend 
 at least forty miles away, underlying the whole district. 
 Diamonds are most abundant where the pipe is surrounded 
 by shales. The author suggests that the carbon for the 
 diamonds was supplied by these shales. If so, the atmo- 
 sphere would be the original source of the diamond, for 
 the plants absorbed carbonic acid from the air, and their 
 remains made the shales carbonaceous. 
 
 These shales belong to the Karoo beds. In Camdebro 
 anthracite occurs in these beds ; perhaps the result of 
 distillation, due to a large dyke which underlies the anthra- 
 cite. 
 
 The dyke-like masses 2 at De Beers differ from the 
 main mass only in being finer grained and less readily 
 decomposed. They are two to three feet thick, and cut 
 through the pipe and the shales and dolerite in all direc- 
 tions. Mr. Dunn also shows that the pipes must be more 
 recent than the dolerite sheets, for the rudely tabular 
 dolerite is tilted up at 40 at the wall of the pipe. In- 
 cluded masses of dolerite also occur in the pipes, which 
 at Bulfontein have been rounded by attrition into boulder- 
 like masses. 
 
 Among recent papers on the diamond regions must be 
 
 1 Quart. Journ. Oeol. Soc. xxxiii. 1877, p. 879. Ibid, xxxvii. 1881, 
 p. 601). 
 
 2 Note by Professor Lewis. The so-called dykes at De Beers are merely 
 harder and finer grained parts of the mass which are not decomposed. 
 Down to 100 feet below the surface, shells, charcoal, &c., have entered into 
 the blue ground. 
 
ON THE HISTORY OF THE DIAMOND 7 
 
 mentioned those of Prof. E. Cohen, of Mr. Hudleston, and 
 of Mr. Dunn. Mr. Hudleston l holds that the matrix of the 
 diamond was a sort of volcanic breccia, which was made 
 hydrous at a considerable depth and ejected in a wet 
 state accompanied by steam, like the product of a mud 
 volcano. The earlier theories as to the origin of the 
 diamond have, in the light of new facts, quite given way 
 to the theory that the diamonds belong to and are part of 
 the matrix in which they lie, and that this matrix is in 
 some way of volcanic origin, either in the form of mud or 
 ashes or lava. 
 
 As the geology of the region has been described by 
 many observers, it may suffice to say that the diamond- 
 bearing pipes penetrate strata of Triassic age which are 
 known as the Karoo beds. Griesbach 2 and Stow 3 in 1871 
 showed that this Karoo formation was penetrated by great 
 interstratined sheets of so-called dolerite, rnelaphyre and 
 amygdaloidal melaphyre, and that below the series of 
 stratified rocks fundamental clay slates and gneisses or 
 granite occurred, which latter came to the surface in Natal 
 and the adjoining regions. The intrusion of the dolerite 
 sheets in the Karoo beds is held to have occurred in a 
 subsequent part of the Triassic period known as that 
 of the Stormberg beds. 4 As Professor Kupert Jones 5 and 
 others have shown, the Kimberley shales belong to the lower 
 Karoo formation. The diamond-bearing pipes penetrating 
 and enclosing fragments of all these formations are thus 
 clearly of upper Triassic or post-Triassic age. 
 
 I now come to the description of the rocks which, 
 through the courtesy of Mr. T. Hedley, in charge of the 
 
 1 Proc. Geol. Assoc. viii. 1883-4, p. 65. 
 
 2 C. L. Griesbach, ' On the Geology of Natal,' Quart. Jo urn. Geol. Soc. 
 xxvii. 1871, p. 53. 
 
 3 G. W. Stow, ' On some points in South African Geology,' Quart. Journ. 
 Geol. Soc. xxvii. 1871, p. 497. 
 
 4 Cape of Good Hope Official Handbook, 1886, p. 83. 
 
 5 Mining Journ. 1886, p. 771. 
 
B 
 
 ON A DIAMOND-BEARING PEEIDOTITE AND 
 
 diamond exhibit at the Colonial Exhibition, I have been 
 able to examine. They come from De Beers Mine, and 
 having been found at a greater depth and in a much less 
 decomposed condition than the specimens primarily ex- 
 amined, it has become possible now, for the first time, to 
 determine the exact nature of the matrix of the diamond. 
 
 The rock occurs in two types, one not bearing diamonds, 
 the other diamantiferous, and the distinction between them 
 is suggestive. Both occur in the same mine, and are dark, 
 compact, heavy rocks, closely resembling one another, and 
 differing mainly in the fact that one is free from en- 
 
 Fici. 2. De Beers Mine, 1885. (Sketch by Professor Lewis from the Colonial Exhi- 
 bition, 1886.) 1* basalt; 2, shale; 3, hard ground; 4, floating reef (true eruptive 
 rock, with more bronzite, no enclosures, no diamonds) ; 5, diamond-bearing rock 
 
 closures of foreign substance, while the other is full of frag- 
 ments of shale and other impurities. It is the latter which 
 is diamantiferous. 
 
 A section of either of these shows that we have to do 
 with a volcanic rock, composed mainly of olivine, and con- 
 taining no felspar, i.e., a peridotite. I will describe first 
 that which is free from inclusions, known as Hard Wack 
 Floating Beef (the word 'reef meaning anything which 
 is worthless). It occurs deep down in the mine, and is 
 a massive black rock. Microscopic examination shows 
 abundant grains of olivine in a remarkably fresh condition ; 
 many of them are rounded, but others show crystalline 
 faces. That olivine is rounded is a common feature, both 
 in volcanic rocks and in meteorites. The cleavages accord- 
 
OAT THE HISTORY OF THE DIAMOND 9 
 
 ing to oo P CD and cc P do are unusually well marked, that 
 according to co P cc being often in straight lines almost 
 as good as in felspar. Olivine is known to occur in rocks 
 in three different habits, according as the rock is granular, 
 porphyritic, or a crystalline schist, as Kosenbusch l has well 
 described. The rock in question contains olivine, with the 
 form belonging to porphyritic rocks. The distinct crystalline 
 shape has been altered by subsequent corrosion. Olivine is 
 the main ingredient of the rock, all other minerals being 
 accessory. 
 
 Of these the principal are enstatite and biotite. The 
 enstatite is clear, not pleochroic, and is readily determined 
 by its parallel extinction ; the biotite is in crystals, which 
 are usually rounded by corrosion, as is indicated by the 
 black rim which often surrounds them. Similar rims are 
 well known around the biotite of many andesites, trachytes, 
 and related rocks. The black rim is shown to be made of a 
 mixture of magnetite and augite, and is thickest when the 
 ground mass is holocrystalline, and thinnest when most 
 glassy. The very thin rims here argue a glassy base. The 
 biotite, as in peridotites and nepheline-basalt, is usually 
 twinned after the law of Tschermak. 
 
 Serpentines with garnet occur as dykes in the Vaal 
 Eiver. Dr. J. Shaw speaks of serpentines, 2 and Professor 
 T. E. Jones of garnets, in Vaal Eiver gravels. 3 Dr. 
 Shaw 4 also states that dykes cross the Vaal Eiver and 
 make rapids. Garnets abound in these gravels, also 
 tourmalines, talc, and mica. 
 
 1 Mikrosk. Pliysiogr. 2 e AufL Bd. i. 1885, p. 410. 
 
 2 Quart. Journ. Geol. Soc. xxviii. 1872, p. 22. 
 
 3 Ibid. p. 18. 4 Ibid. p. 21. 
 
10 THE MATRIX OF THE DIAMOND 
 
 SECTION II 
 
 THE MAT MIX OF THE DIAMOND 
 
 BY H. CARVILL LEWIS, M.A., F.G.S. 
 
 (Read at the Meeting of the British Association at Manchester, 1887) 
 
 AT the last Meeting of this Association l I had the honour 
 of giving a short description of the remarkable rock which 
 forms the matrix of the diamond in South Africa. Since 
 then, as I have received fresh material, it has been possible to 
 study it carefully, both microscopically and chemically, and 
 to compare the geological features of Kimberley with those 
 of other diamond localities in various parts of the world. 
 
 Without repeating what was then said, I will merely 
 remind you that the diamond-bearing rock was shown to 
 be an eruptive neck of post-Triassic age, penetrating and 
 enclosing fragments of Karoo shales, and that this rock is 
 a porphyritic peridotite of peculiar structure, closely ana- 
 logous to a similar rock in Elliott Co., Kentucky. 2 
 
 The rock, which was obtained from a depth of about 
 500 feet, is much less decomposed than the material 
 usually obtained in the diamond mines, and both its 
 composition and structure can be readily studied under the 
 microscope. 
 
 It is a dark-green heavy rock, resembling a dense 
 serpentine, in which one sees with the naked eye glistening 
 plates of brown biotite, small deep-red garnets, and large 
 dark-green crystals or grains of olivine and bronzite. 
 
 1 At Birmingham, 1886. Brit. Assoc. Report, 1886, p. 667. 
 
 2 For a description of this rock, see Section III. 
 
THE MATRIX OF THE DIAMOND 11 
 
 The last two minerals being of identical colour with the 
 rest of the rock are not so conspicuous as the first two. 
 Scattered through the whole rock are a large number of 
 angular fragments of altered black shale. These are often 
 so abundant as to give the rock a brecciated appearance. 
 The rock takes a good polish, and, on such polished sur- 
 faces, the olivine is clearly seen to be the predominating 
 mineral, and to occur in porphyritic crystals, lying in a 
 ground-mass of serpentine. Traces of fluidal structure are 
 also seen in polished specimens. The rock resembles, 
 externally, certain dark picrites, like those of Tringenstein 
 or Schriesheim, yet even its general appearance is different 
 from that of any other known rock. 1 
 
 The rock from Kentucky has the same characters, 
 though containing less numerous foreign fragments. 
 
 We now proceed to the more exact description of this 
 reck. We will consider (1) the minerals of which it is com- 
 posed, (2) its chemical composition, (8) its structure, (4) its 
 geological characters and significance. 
 
 (1) CONSTITUENT MINEKALS 
 
 The following minerals occur in the Kimberley rock, 
 many of them being detected only under the microscope. 
 
 Olivine, forming the larger portion of the rock, often 
 quite fresh. 
 
 Enstatite, chrome-diopside, smaragdite and bastite, often 
 in fine green plates or crystals. 
 
 Biotite, a very prominent ingredient. 
 
 Garnet, common in bright red grains. 
 
 Pefovskite, abundant in microscopic crystals. 
 
 Magnetite, chromite, ilmenite, picotite, common under 
 the microscope. 
 
 Apatite, epidote, orthite, tremolite, tourmaline, rutile, 
 sphene, leucoxene (scarce and minute). 
 
 1 So far as my knowledge goes, this remark, though written almost ten 
 years ago, still holds good. A general idea of the aspect of the rock may be 
 obtained from Plate I. T. G. B. 
 
12 THE MATEIX OF THE DIAMOND 
 
 Serpentine, calcite, zeolites, chalcedony, and talc, as 
 decomposition products. Also an undetermined mineral, 
 probably cyanite, and finally diamond (scarce). 
 
 Olivine. Olivine forms the most abundant constituent 
 in the rock, occurring in porphyritic crystals or rounded 
 grains, which may attain considerable size. These crystals 
 are sometimes over a centimetre in diameter, though 
 usually of smaller dimensions, and are sprinkled plentifully 
 in a serpentinous base. The dark-green colour is so nearly 
 that of the whole rock that the olivine is not so conspicuous as 
 the mica, although, as seen in thin sections, it is much more 
 abundant. Many of the crystals are comparatively fresh, 
 with the hardness and lustre of unaltered olivine. Others 
 are partly changed into serpentine, while others, again, are 
 entirely replaced by serpentine. 
 
 Except an occasional grain of a spinellid or, more 
 rarely, enstatite, the fresh olivine is pure and free from 
 solid enclosures. Occasionally bubble-like inclusions of 
 gas or glass occur, in the form of minute elongated rounded 
 cavities. These are often aggregated together in plant- 
 like growths, such as are not uncommon in the olivine of 
 a porphyritic eruptive rock. They also occur in strings 
 traversing the crystal. With a high power these inclusions 
 are seen to be of a brown colour resembling glass (negative 
 crystals ?). The interesting changes which Prof. Judd 1 has 
 shown to occur in the olivine of deep-seated rocks, whereby 
 secondary enclosures are produced, through the process 
 which he has called ' schillerisation,' are entirely absent 
 here. 
 
 An unusual feature in the olivine of the Kimberley 
 rock is its perfect cleavage. This cleavage is so perfect that 
 in ordinary light the mineral would be at once designated 
 as bronzite or diallage. In polarised light the high double 
 refraction distinguishes it from enstatite, and the parallel 
 extinction from diallage or diopside. This cleavage is 
 
 > Quart. Journ. Geol Soc. xli. 1885, p. 362. 
 
THE MATRIX OF THE DIAMOND 
 
 13 
 
 parallel to the brachypinacoid (ooPoo), an optic axial 
 bisectrix appearing in sections with the most marked 
 cleavage. * ." 
 
 PIG. 3. Olivine crystal seen parallel to ooPoo and showing excellent cleavage along 
 co P , and poorer cleavage along OP. The filiar bastitic mineral into which it is 
 altered has fibres parallel to the principal cleavage. A bisectrix occurs at right 
 angles to the section, and the plane of the optic axis is parallel to the base 
 
 There are also secondary cleavages, and the usual 
 irregular cracks so common in olivine. 1 
 
 Olivine has not been detected in the ground mass of 
 this rock. It is usually in the form of crystals, more or 
 less rounded and corroded, and even when completely 
 changed to serpentine, the original crystalline form can 
 generally be recognised. 
 
 Corrosion cavities (the * einbuchtungen ' of the -Ger- 
 mans) are sometimes seen in the olivines. 
 
 The following are some of these : 
 
 FIG. 4. Corrosion cavities 
 
 FIG. 5. CoiTOsion cavities 
 
 Zirkel, MiJtrosk. Bescha/. der Min. 1873, p. 214. 
 
14 THE MATRIX OF THE DIAMOND 
 
 The olivine alters by decomposition either into serpen- 
 tine, or into tremolite, or into a bastitic fibrous mineral. 
 The alteration into serpentine proceeds in the usual manner, 
 beginning at the outer edge and in cracks in the crystal, 
 and gradually penetrating deeper, as new cracks are formed, 
 until the change is complete. A homogeneous nearly 
 isotropic serpentine is the final result. Fibrous serpentine 
 or chrysotile also forms around the olivine grains, and in 
 this case the chrysotile fibres stand more or less at right 
 angles to the original faces of the crystal. The chrysotile 
 is much more highly doubly refracting than the compact 
 serpentine, which latter, when most dense, is often nearly 
 isotropic. Another serpentinous mineral is faintly pleo- 
 chroic in pale shades of green, and is, perhaps, more nearly 
 related to bastite. 
 
 Tremolite (fig. 6) in the form of asbestos occurs as a 
 secondary mineral pseudomorphic after olivine. It fre- 
 quently happens that while serpentinisation begins at the 
 outside of a crystal, fibrous tremolite begins growing within, 
 finally forming a mass of asbestiform fibres surrounded by 
 a zone of green serpentine. These asbestos fibres often 
 grow partly parallel to the vertical axis, and partly parallel 
 to the domes of the olivine. They are distinguished from 
 other minerals by their high colour in polarised light, and 
 by vertical fibres separated by partings or cleavages like 
 those which divide sillimanite, and by an obliquity of 
 extinction at about 15. They are perfectly colourless and 
 non-pleochroic. A fibre may be compact in the centre or 
 at one end, and at the other end may be fringed out into 
 fine hair-like asbestos. 
 
 In the second figure (7) two olivine crystals have grown 
 side by side, their axes parallel. A thin green rim of 
 serpentine surrounds each crystal. A round grain of olivine 
 remains in each, and crystals of tremolite surround it. 
 Between the tremolite and the serpentine is a pseudomorphic 
 mass of talcose substances, in which lie rutile needles 
 parallel to the faces of the crystal. 
 
THE MATRIX OF THE DIAMOND 
 
 15 
 
 Another kind of alteration, rare in the Kimberley rock, 
 but very common in the Kentucky variety, is into a 
 peculiar finely fibrous substance of dark blue colour. 
 The olivine is never wholly changed into this material, 
 which appears only at the two extremities of a crystal or 
 along cracks. The fibres always stand parallel to the 
 cleavage planes of the olivine, and seem to be due to a 
 finer splitting up of these cleavage planes until they 
 become fibrous. This fibrous substance is faintly pleo- 
 
 "P 
 
 Fio. 6. Diagrammatic, r, rutile needles ; 
 tr, tremolite ; ch, chrysotile ; m, magnetite 
 or chroinite ; p, perovskite 
 
 FIG. 7. Diagrammatic. , serpentine: 
 tr, tremolite ; o, oliviue ; r, rutile 
 
 chroic like bastite, and seems to be a new variety of that 
 mineral. (It is seen only in the Kentucky rock.) Dr. 
 Eosenbusch suggested to me that it resembled the ' aerinite ' 
 of Lasaulx, 1 also a product of alteration. It will be more 
 fully treated under the description of bastite. The un- 
 usually perfect cleavage in the olivine is particularly well 
 developed near the edges, where the fibrous substance is 
 formed. This alteration is at the edges of otherwise 
 
 Neues Jahrb. 1876, p. 352 ; Bull. Soc. Min. de France, i. 1878, p. 125. 
 
16 
 
 THE MATRIX OF THE DIAMOND 
 
 perfectly fresh olivine, and appears to be an incipient stage 
 of serpentinisation. 
 
 The alteration into serpentine is shown in figures 8 
 and 9 ; and into the chloritic mineral in figure 10. *- 
 
 FIG. 8 
 
 FIG. 9 
 Alterations of olivine 
 
 FIG. 10 
 
 The most interesting result of the serpentinisation of 
 the olivine is the production of secondary rutile. Rutile 
 never appears in the fresh olivine, but as serpentinisation 
 begins rutile needles form along the border of the de- 
 composing olivine, their longer axes being parallel to 
 the outlines of the original crystal. When serpentinisa- 
 tion has proceeded so far that only an inner kernel of 
 olivine remains, rutile needles may be formed all around 
 this inner kernel, lying in the serpentine pseudomorph, 
 not irregularly as if ordinary enclosures, but in fixed crys- 
 tallographical directions parallel to the olivine outlines. 
 Figures 11 to 15 exhibit this secondary rutile. 
 
 FIG. 11 
 
 FIG. 12 
 Rutile in olivine 
 
 FIG. 13 
 
 The rutile needles have originated within from small 
 particles of titanic iron enclosed in the olivine, or from 
 
THE MATRIX OF THE DIAMOND 
 
 17 
 
 titanic acid in its composition. Sometimes a grain of 
 titanic iron can be seen imbedded in the rutile needles, as 
 in fig. 16. The rutile crystals are rarely geniculated. 
 
 Fir;. 15. Id. FIG. 16. (with titanic iron) 
 
 The production of secondary rutile through the decom- 
 position of olivine does not appear to have been previously 
 noticed, although in decomposing phlogopite or biotite l it is 
 a not uncommon occurrence, and its association with 
 titanic iron 2 is well known. One of the most interesting 
 and unusual features of the olivine in this rock is that it is 
 younger than or contemporaneous with the chrome diop- 
 side and bronzite. Bronzite occurs enclosed within it, but 
 olivine has not been observed enclosed within the bronzite. 
 When thus enclosed in the olivine the bronzite is of more 
 or less rounded form. 
 
 In fig. 17, a rounded grain of clear diopside with good 
 cleavages or partings is enclosed in fresh olivine (Kentucky 
 peridotite) . 
 
 d 
 
 FIG. 17. Kentucky peridotite. d, diopside ; FIG. 18. e, enstatite, with specks 
 o, olivine of biotite 
 
 1 Cohen, Neues Jahrb. 1882, ii. p. 194. 
 
 2 Cathrein, Zcits. fur Kryst. vi. 1882, p. 244 ; Lasaulx, Zelts. fur Kryst. 
 viii. 1884, p. 54. 
 
 G 
 
18 THE MATRIX OF THE DIAMOND 
 
 In fig. 18, the enclosed mineral is enstatite, distinguished 
 from the diopside by much lower double refraction and by 
 parallel extinction. The enstatite here encloses secondary 
 biotite scales, and the biotite in turn contains small' hexa- 
 gons of hematite. 
 
 As is well known, olivine is almost always older than 
 the more acid pyroxene in any given rock. Unless we sup- 
 pose that a subsequent fusion has produced it, or that there 
 is a secondary olivine, there would appear to be an excep- 
 tion here to the useful and generally applicable rule that the 
 constituents of a magma crystallise out in the order of 
 diminishing basicity. 1 According to Hussak, 2 augite and 
 hornblende occur enclosed in olivine in the picrite-porphy- 
 rite of Steierdorf, Banat, and the enclosure of enstatite in 
 olivine is often seen in meteorites. It is probable that 
 these are cases of contemporaneous crystallisation. 
 
 A highly refracting rhombic mineral, resembling olivine, 
 also occurs in some remarkable zones which surround the 
 bronzite in the Kimberley rock, and which have the appear- 
 ance of contact-fusion zones. These zones, in which the 
 olivine makes a pegmatitic or * eozoonal ' structure, as in 
 the chondri of meteorites, will be discussed more fully under 
 the description of enstatite. They may be the rudimentary 
 stage of the compact olivine enclosing enstatite, and point 
 to the contemporaneous and rapid crystallisation of olivine 
 and enstatite a common occurrence in meteorites. 
 
 The significance of olivine as a characteristically igneous 
 mineral, and as one readily produced by dry fusion, is well 
 known. 3 It is a mineral of special interest, as regards the 
 part it plays in connecting deep-seated terrestrial rocks with 
 those of celestial origin. 4 As the predominating constitu- 
 ent of the present rock, it places this clearly among the 
 
 Rosenbusch, Neues Jahrb. 1882, ii. p. 7. 
 
 2 Verhandl. der geol. Beichsanstalt, 1881, p. 260. 
 
 3 Bourgeois, Reproduction Artificielle des Mindraux, Paris, 1884, p. 108. 
 
 4 Daubree, Etudes Synthdtiques de Geologic Exptrimentale, Paris, 1879, 
 p. 538 ; Wadsworth, Lithologlcal Studies, 1884, p. 84. 
 
THE MATRIX OF THE DIAMOND 19 
 
 peridotites, while the idiomorphic character of the crystals, 
 and the evidence of the action of a corrosive magma upon 
 them, class the peridotite among the volcanic rather than 
 the plutonic series. 
 
 Pyroxenic Minerals. Three clear green minerals, almost 
 identical macroscopically, occur in the peridotite of Kimber- 
 ley, and are found loose in the decomposed ' blue ground.' 
 These are smaragdite, bronzite, and chrome diopside or dial- 
 lage. These minerals are so hard and clear and free from 
 inclusions that they have been cut as gems. They all have a 
 light grass green colour, and are unattacked by acid, and 
 all sink in a Thoulet's solution, having a specific gravity 
 of 3. They can be distinguished from each other by specific 
 gravity, by blowpipe tests, and especially by optical means. 
 All are coloured by chrome oxide, as is shown by blowpipe 
 tests. 
 
 Smaragdite. This has the hornblende cleavage, and an 
 extinction of about 15. It has a fine green colour, and in 
 thin sections it is pleochroic in shades of green. The 
 mineral has been analysed by Maskelyne and Flight, who 
 found the composition of loose fragments in the blue ground 
 of Du Toits Pan to be as follows : 
 
 Si0 2 . . ... . . 52-97 
 
 Al a 3 (with Cr 2 3 ) . . . 1-94 
 
 FeO 4-52 
 
 CaO 20-47 
 
 MgO . '. . . . 17-49 
 
 Na 2 . . . . . 1-77 
 
 H 2 0. * . v . . 0-58 
 
 99-74 
 
 Bronzite and Bastite. Of the three related green 
 minerals in the peridotite, bronzite is the most abundant. 1 It 
 
 1 In the specimens from Kimberley, examined by Miss Raisin and my- 
 self (Geol. Mag. 1895, p. 496), the green mineral in most, if not in all, cases 
 was not an enstatite, but an augite. T. G. B. 
 
 c 2 
 
20 THE MATRIX OF THE DIAMOND 
 
 occurs in crystals or crystalline plates with the characteristic 
 fine striation of enstatite, parallel to the vertical axis. It 
 has a weaker double refraction than the other two minerals, 
 its colours in polarised light being of the first order. It 
 gives parallel extinction, and the cleavage plates show no 
 hyperbolas. The plane of the optical axes is parallel to the 
 cleavage. The colour is a paler green than that of the 
 other two minerals. Before the blowpipe it is infusible, or 
 nearly so. The specific gravity, as determined in Klein's 
 cadmium solution, was 3*199. Maskelyne and Flight l have 
 analysed loose fragments from the 'blue ground' of Du 
 Toits Pan, as follows : 
 
 Si0 2 55-91 
 
 A1 2 3 2-64 
 
 Cr 2 3 ..... 0-54 
 
 FeO. . . . . 4-99 
 
 NiO ...... trace 
 
 MgO ..... 34-91 
 
 CaO 0-45 
 
 99-44 
 
 They draw attention to the resemblance of this bronzite 
 to that in the meteorite of Breitenbach. If, with Tschermak, 2 
 we draw the line between bronzite and enstatite at a con- 
 tent of 5 per cent, of iron protoxide, it will be seen that 
 our mineral is just on that line ; and thus, as having an 
 intermediate composition, may be called with equal pro- 
 priety either bronzite or enstatite. 
 
 The bronzite sometimes alters into biotite, which may 
 occur in it in scales or plates which appear to be secondary. 
 It also alters into bastite, which often entirely replaces the 
 bronzite, and may be quite an abundant constituent. Bastite 
 is distinguished from bronzite by a faint yellowish colour, 
 
 1 Quart. Journ. Geol. Soc. xxx. 1874, p. 411. 
 
 2 Lehrb. der Mineralogie, Wien, 1885, p. 443. 
 
THE MAT BIX OF THE DIAMOND 21 
 
 weak pleochroism, and by the appearance of a bisectrix in 
 cleavage flakes. The plane of the optic axis is parallel to 
 the fibres, and there is parallel extinction. It has a some- 
 what more fibrous character than bronzite, and with the 
 latter forms the most abundant constituent of the rock 
 after olivine. 
 
 The blue fibrous substance which forms an alteration 
 rim around olivine has already been mentioned. This 
 peculiar mineral, common in the Kentucky rock, has a 
 dark indigo colour, and is faintly pleochroic, being dark 
 indigo blue when the nicols are parallel to the fibres, and 
 light greenish blue when at right angles (c > b or ). 
 The plane of the optic axes is parallel to the fibres and the 
 c axis and c = r. The blue colour disappears on heat- 
 ing the slide in acid, and the mineral is gelatinised. All 
 these are the characters of bastite. In some cases it is 
 almost isotropic, while in other cases some of the fibres 
 have a double refraction nearly as high as enslatite, the 
 tints rising nearly to yellow of the first order. In colour it 
 somewhat resembles glaucophane. 
 
 Bastite is well known as an alteration product of bronzite, 
 but has not previously been observed as a result of the 
 change of olivine. From this circumstance, and from its 
 deep blue colour, it may be justly considered as a new 
 variety of bastite. 1 
 
 Chrome-diopside. The chrome-diopside has a fine 
 emerald green colour, richer than that of the other two 
 minerals. The specific gravity is higher than that of 
 bronzite, being 3*267 (determined in cadmium solution). 
 Its ready fusibility before the blowpipe, and its much higher 
 colours in polarised light, also distinguish it from the 
 bronzite. Cleavage fragments show a very faint pleochroism, 
 not nearly as distinct as that of smaragdite, and an extinc- 
 
 1 I have occasionally observed a blue tinge, almost lite a stain, and 
 generally similar to this, in examining dark -coloured serpentines. I doubt 
 whether its value is so great as to constitute a variety. T. G. B. 
 
22 THE MAT BIX OF THE DIAMOND 
 
 tion angle of 39. In converging polarised light an axis 
 appears on cleavage fragments which are parallel to oo Fob 
 
 Three cleavages or partings, each well developed, also 
 occur in chrome-diopside, so that it readily cleaves into 
 almost cubical rhombs. It has an excellent cleavage 
 parallel with oo Poo , another, less perfect, parallel with 
 oo Poo , and another parallel with OP. This last is the 
 salite parting, and not a true cleavage. It is probably, as 
 Tschermak, 1 Yom Kath, 2 and others have shown, due 
 to the interposition of thin twinning lamellae parallel 
 to the base, and the mineral might be called a salite. 
 Von Koksharow 3 speaks of the ' zusammensetzungfliichen ' 
 in chrome-diopside from the Urals as often confounded 
 with true cleavage faces. The ordinary augitic prismatic 
 cleavage is not apparent microscopically on these basal 
 parting sections, but the pinacoidal cleavages are seen as 
 fine lines crossing each other at right angles and parallel 
 to the sides of the section. 
 
 A cleavage fragment gave the angles oo Poo A P = 106, 
 and oo Poo A P = 90. 
 
 The face of the best cleavage, parallel to oo Poo has a 
 pearly lustre, and is nearly or quite free from striae. The 
 orthopinacoidal cleavage plates are striated vertically, and 
 show in convergent light a single axis identical with that 
 seen in cleavage plates of diallage. 
 
 The low extinction angle, 39, is typical of a pure lime- 
 magnesia diopside, free from iron, for both iron and mag- 
 nesia, as Tschermak, 4 Wiik, 5 Herwig G and Doelter 7 have 
 shown, tend to increase the extinction angle. The so- 
 called omphacite, occurring in eclogites, peridotites, olivine 
 bombs, and serpentines, seems to be but another name for 
 
 Min. Mitth. 1871, p. 22. 2 Zeits. fiir Kryst. v. 1881, p. 495. 
 
 Materialien zur Mincralogie Russlands, iv. 1862, p. 259. 
 
 Min. Mitth. 1871, p. 22. 
 
 Finska Vetensk. Soc. Forhandl. xxiv. 1882, p. 33 ; xxv. 1883, p. 109. 
 
 Programme des Gymw. Saarbriicken, Nr. 416, 1884. 
 
 Neues'Jahrb. 1885, ii. p. 43. 
 
THE MAT BIX OF THE DIAMOND 23 
 
 cbrome-diopside, the composition and optical characters 
 being identical. 1 
 
 Chrome-diopside gives birth to granular calcite, which 
 always accompanies it when decomposed. When there is 
 any doubt in the section as to whether a mineral is bronzite 
 or chrome-diopside, the presence of calcite on its edges 
 and in its cracks is often a sufficient criterion for diopside. 
 The composition is probably that of the pure diopside 
 molecule, CaO, MgO, 2Si0 2 . 
 
 Chrome-diopside is well known to occur with enstatite 
 in dunite, in Iherzolite and in other peridotites and ser- 
 pentines, and4n the ' olivine bombs ' which are enclosed 
 in basalt. Descloiseaux has described a chrome-diopside 
 in the platiniferous (and diamantiferous ? ) peridotite of 
 Nischne-Tagilsk, Urals. 
 
 Fluid or glass inclusions, resembling those in the olivine, 
 were noticed in cleavage fragments of the chrome-diopside, 
 which were otherwise pure. 
 
 The fact has already been pointed out that bronzite and 
 chrome-diopside occur sometimes enclosed in olivine, and 
 sometimes surrounded by what seems to be a fusion zone. 
 This fusion zone or growth zone has a peculiar worm- 
 like radiating structure, which may be compared with 
 that of the kelyphite rim 2 around garnets in serpentine, or 
 the radial zones around olivine in certain norites 3 and 
 gabbros, or the so-called granophyric 4 or pegmatitic 5 
 structure in some quartz-porphyries, or the struc- 
 ture in the chondri of meteorites. 6 The principal 
 mineral in these zones is a colourless substance, in short 
 worm-like forms, with a high index of refraction, high 
 
 1 Schrauf , Zeits. fiir Kryst. vi. 1882, p. 329. 2 Ibid. p. 358. 
 
 3 Tornebohm, Neucs Jahrb. 1877, p. 383 ; Becke, Min. und Petr. 
 Mitth. iv. 1882, p. 450 ; Adams, American Naturalist, 1885, p. 1087. 
 
 4 Rosenbusch, Mikrosk. Physiogr. ii. 1887, p. 383. 
 
 5 Michel Levy, Bull. Soc. Geol. France, iii. 1875, p. 199; Ann. dcs 
 Mines, viii. 1875, p. 337. 
 
 6 Wadsworth, Litholoyical Studies, 1884, p. 89. 
 
24 THE MATRIX OF THE DIAMOND 
 
 double refraction, positive character, parallel extinction, 
 and with traces of vertical and basal clea\age. The axis 
 of greatest elasticity is at right angles to the best cleav- 
 age (b= ). The high colours in polarised light are identi- 
 cal with those of olivine, and serpentine sometimes replaces 
 it. All these characters point to olivine as the mineral 
 forming the greater part of the zone. These olivine prisms 
 are all rounded, and radiate irregularly from the central 
 bronzite. They are imbedded in a nearly amorphous 
 glass-like brown serpentinous substance, and are accom- 
 panied by small quantities of calcite, and of a mineral 
 with a high index of refraction, but very low double refrac- 
 tion, which occurs in rectangular prisms, has traces of a 
 cleavage in partings parallel to the base, and is negative. 
 This microlith, however, was noticed only in a few cases. 
 Olivine, it seems, is the main constituent of these zones. 
 The grains are generally so minute and crowded together 
 that they form a grey highly refracting fibrous border or 
 fringe around the enstatite, like leucoxene around titanic 
 iron. Farther away from the enstatite the grains become 
 larger and more worm-like, so that they can be separately 
 studied. The structure of these zones resembles that figured 
 by Becke, 1 as occurring around garnets in a garnet-olivine 
 rock from Karlstatten, Lower Austria, and called by him 
 ' centric ' structure. He has figured a similar structure 
 in the omphacites of certain eclogites, 2 and speaks of it as 
 ' darmzottenahnlich.' 3 
 
 It has often been called a pegmatitic or micro-pegma- 
 titic structure, since, in many instances, a number of the 
 grains have the same orientation, extinguishing simultane- 
 ously, the two substances being contemporaneously crystal- 
 lised. This is also the case, to a limited extent, in the 
 zones under consideration. Perhaps the term centro- 
 pegmatitic would more nearly express it. From its 
 
 1 Min. und Petr. Mitth. iv. 1882, p. 326. (See Plate II. figs. 2 and 3.) 
 
 2 Loc. cit. p. 319. (Plate III. fig. 15.) 3 Ibid. p. 322. 
 
THE MATRIX OF THE DIAMOND 25 
 
 resemblance to organic alga-like forms it might also be 
 called ' eozoonal.' More nearly allied, however, than any of 
 these is a peculiar structure, often found in meteorites, 
 for it is a phase of the so-called chondritic structure. As 
 will subsequently appear, our rock has some close resem- 
 blances, both in composition and structure, to certain 
 meteorites ; the structure of the zone that we are now 
 attempting to describe has frequently been observed in 
 meteorites, and has given rise to various conjectures. 
 
 In the Kentucky rock I have noticed the same peg- 
 matitic olivine zones around the enstatite. The olivine 
 grains in these zones are imbedded in a brown, nearly 
 isotropic, substance, which suggests a serpentinised glass 
 or base. 
 
 Mica. The mica is, next to the olivine, the most 
 abundant mineral, and in hand specimens it is the most 
 conspicuous mineral. When the rock has been exposed to 
 the weather it appears sprinkled with glittering mica 
 crystals which, when weathered, form silvery spangles on 
 the black rock. The ' blue ground ' and the soil about the 
 diamond diggings, both at Kimberley and on the Yaal 
 river, contain many fragments of mica, which is thus re- 
 garded as the principal indication of diamonds. In the 
 rock which we are describing it is of a dark red-brown 
 colour, like biotite or phlogopite, and is apparently quite 
 fresh and undecomposed. Plates half a centimetre in 
 diameter are very common, and sometimes pieces occur 
 two centimetres in diameter. It is brittle when fresh. 
 Before the blowpipe this mica melts quietly to a dark 
 glass sometimes slightly exfoliating. 
 
 Under the microscope the mica is seen to be nearly 
 pure and unaltered. It occurs usually in thick isolated 
 plates or crystals, lying like the olivine porphyritically in 
 the ground mass. These are frequently polysynthetically 
 twinned, according to the law so ably expounded by Tscher- 
 mak. It is indicated by the different absorption in the 
 alternate layers. The extinction angle between the two 
 

 26 THE MAT BIX OF THE DIAMOND 
 
 alternate striae is about 10, showing an extinction for single 
 lamellae of 5. 
 
 The mica seldom occurs in well bounded crystals, being 
 more usually found in irregular plates. Sometimes the 
 crystals are corroded, as if from a re-solution of the magma. 
 Sometimes also a narrow rim of ' opacite ' surrounds the 
 mica, this being particularly observable in such crystals as 
 have been greatly corroded and rounded. This black rim 
 (the * opacit rand ') is never thick, and is only sometimes 
 present. Sometimes the edges of the mica crystals are 
 curved, this being the result of motion in the rock. In 
 certain cases the mica is found to contain very small 
 short thick rods of a highly refracting dark red substance, 
 probably rutile. These rutile needles lie parallel to the 
 base, and are probably a result of the partial decomposition 
 of the mica. They indicate that the mica contained a 
 small percentage of titanium. The production of rutile as 
 a secondary mineral has been frequently observed in mag- 
 nesia-mica. 1 
 
 Another mode in which the mica occurs is around the 
 garnets in the rock. Sometimes a large red pyrope will be 
 entirely surrounded by a narrow zone of brown mica. 
 
 A third method of occurrence of the mica is in the form 
 of small scales in enstatite, here apparently due to the 
 alteration or corrosion of that mineral. This was noticed 
 in only a few instances, and especially in those in which the 
 enstatite was enclosed in olivine. In one instance, small 
 scales of magnesia mica alone were enclosed in olivine, as 
 though the original enstatite had been entirely replaced 
 by the mica. 
 
 A fourth association in which we find magnesia-mica 
 is as a product of the apparent fusion or metamorphism of 
 
 1 Kosenbusch, Mikrosk. Physiogr. i. 1885, p. 483 ; Dathe, Zeits. Deutsch. 
 Geol. Gesell. xxxiv. 1882, p. 35 ; Cross, Min. und Petr. Mittli. iii. 1881, 
 p. 372 ; Zirkel, Ber. der Sachs. Gesell. dcr Wiss. 1875, p. 202 ; Kalkowsky, 
 Die Gneiss -Formation des Eulengcbirgcs, 1878, p. 28; Williams, Ncues 
 Jahrb. Beil. Bd. ii. 1883, p. 617. 
 
THE MATEIK OF THE DIAMOND 27 
 
 enclosed fragments of shale or other rocks. These enclosures 
 are sometimes entirely altered into a nearly opaque dirty 
 grey aggregate, largely composed of a pleochroic mica, ap- 
 parently an impure scaly biotite. These mica scales are 
 highly pleochroic, and are, perhaps, another mica than 
 that which composes the large porphyritic crystals, for the 
 latter seem to be primary constituents of the rock. By 
 decomposition or serpentinisation the mica is altered into an 
 irregular mass of sericite, or talc- scales, in which round or 
 oval masses of an apparently isotropic gum-like substance 
 occur. 
 
 The optical characters of the mica are unusual. Un- 
 like ordinary biotite, it has a weak pleochroism. As a 
 prismatic section is revolved over the polariser the light 
 brown colour, while varying in intensity, does not become 
 dark. Similar weakly pleochroic magnesia-micas have been 
 observed in other ultra-basic rocks. Zirkel l noticed such 
 a mica in the leucitite of the Leucite hills, Wyoming 
 territory ; and Judd 2 has described an altered magnesian 
 mica with feeble pleochroism in the ' Scyelite ' of Caith- 
 ness. 3 The mica in the Kimberley rock has the usual 
 index of refraction and high double refraction ; it has a 
 very small optic axial angle, and is a mica of the second 
 order. The ' strike figure ' has one ray parallel to the 
 symmetry plane, and to the plane of the optic axes. Opti- 
 cally, therefore, it is a meroxene or phlogopite. 
 
 Maskelyne and Flight 4 have analysed this mica in a 
 decomposed state. In the soft ' blue ground ' of Du Toits 
 Pan this mica in decomposing has absorbed much water 
 and become a vermiculite, exfoliating when heated. To 
 this substance Maskelyne and Flight have given the 
 
 1 ' Microscop. Petrogr.' U.S. Geol Expl. 40th Par. vi. 1876, p. 261. 
 
 2 Quart. Journ. Gcol. Soc. xli. 1885, p. 405. 
 
 3 [I have observed a rather similar mica in a picrite from Sark, which 
 presents a considerable resemblance to scyelite. Geol. Mag. vi. 1889, p. 110. 
 T. G. B.] 
 
 4 Quart. Journ. Gcol. Soc. xxx. 1874, p. 409. 
 
28 THE MATRIX OF THE DIAMOND 
 
 name of ' Vaalite.' In this state it is a soft yellow or bluish- 
 green micaceous mineral, containing nearly 10 per cent, of 
 water. 
 
 The following is the composition of the * Vaalite ' : 
 Si0 2 . . . . 40-83 
 
 A1 2 3 ..... 9-80 
 
 Fe 2 3 6-34 
 
 Cr 2 3 ..... trace 
 MgO . . . . . 31-34 
 
 Na 2 0-87 
 
 H 2 9-72 
 
 99-20 
 
 Garnet. Deep-red rounded grains of clear pyrope are 
 abundant in the ' blue ground,' and these, with black grains 
 of titanic iron, remain with the diamonds in the final wash- 
 ings. Pyropes are also seen imbedded in the dark green 
 peridotite rock. They have been utilised as gems. The 
 pyropes which were observed in thin sections were isotropic, 
 nearly pure and always rounded. In one case a pyrope 
 was surrounded by a zone of magnesia-mica. Cracks 
 penetrate the pyropes irregularly, as is usual. 
 
 Another variety of garnet occurs, which greatly resem- 
 bles the diamond. These garnets are very small, colourless, 
 or with a faint tinge of green, and have such a high index 
 of refraction that it is difficult to see their shape. They are 
 crystallised apparently in forms strongly suggesting the dia- 
 mond, the faces being sometimes curved, and the octahedral 
 forms apparently predominating. They are unattacked by 
 acids, including hydrofluoric acid. They melt readily to 
 glass in a crucible, and may thus be distinguished from dia- 
 monds. Most of them are so small as to be seen only with 
 high powers, and they are then readily confounded with 
 minute diamonds. They probably belong to the variety of 
 garnet called * demantoid,' 1 which is found in the diamond 
 
 1 Eammelsberg, Zeit*. Deutsch. Geol. Gesell. xxix. 1877, p. 819. 
 
THE MATRIX OF THE DIAMOND 29 
 
 region of Syssersk, Urals, imbedded in serpentine. 1 Other 
 small garnets, again, of bluish-green colour, giving a chrome 
 reaction, may belong to the variety named ' ouvarovite.' 
 
 The pyropes are about as abundant as in the garnet- 
 bearing serpentines, and it is probable that many of these 
 serpentines have been derived from a peridotite of similar 
 nature to that now under consideration. These serpentines 
 are related not merely in the occurrence of garnet, but also 
 in the association of olivine, bronzite, diallage and some- 
 times perovskite, and even diamond. 
 
 Perovskite. Perovskite is an abundant and charac- 
 teristic mineral in the rock under consideration. It occurs 
 in crystals, in crystalline aggre- 
 gates, and in combination with ^ / *- 
 
 ilmenite. It was isolated with the j/ Y' 
 garnets from the other constituents 
 by treatment with sulphuric and 
 hydrofluoric acids, and submitted 
 to blowpipe tests. Most of the 
 mineral thus isolated was in the 
 form of brownish-black cubical crys- FlG . ]9._p er ovskite 
 
 tals, with octahedral truncations 
 
 (fig. 19). These crystals were almost all of a nearly uniform 
 size. In the thin sections the perovskite appeared as reddish- 
 brown crystals or aggregates, deep yellow when thin, but 
 sometimes nearly opaque, scattered abundantly through 
 the ground-mass. In their deep colour and very high index 
 of refraction they resembled the rutile grains of the 
 crystalline schists, but were readily distinguished from that 
 mineral or from zircon by their remarkably low power of 
 double refraction. The colour in polarised light seldom 
 rose above grey of the first order, and was sometimes as 
 high as white of the first order. The characteristic optical 
 properties therefore are an index of refraction nearly as 
 
 1 Losch, Neues Jahrb. 1879, p. 785 ; Verhandl. der Buss. Miner. Gesell. 
 xiii. 1878, p. 432 ; xvi. 1881, p. 299. 
 
30 THE MATRIX OF THE DIAMOND 
 
 high as rutile (over 2) and a power of double refraction 
 about as low as zoisite (7 a = *005). The low double 
 refraction, together with the opacity often caused by in- 
 clusions of ilmenite or chromite, might in some cases cause 
 it to be mistaken for a dark spinel or other isotropic 
 mineral. In no case, however, is the perovskite isotropic. 
 Extinction always occurs parallel to the diagonal of the 
 cube. Pleochroism is extremely faint. The form and 
 optical properties of the perovskite show that in all cases it 
 belongs to the rhombic system, and is in the form of twins, 
 or of aggregates of twins. The commonest form is that 
 of interpenetrative twins, so crossed as to form a cube. 
 The following are common forms as seen in ordinary 
 light:- 
 
 FIG 20 
 
 
 FIG. 21 FIG. 22 FIG. 23 
 
 FIGS. 20-23. Twinned perovskite 
 
 A cleavage or parting occurs parallel to the cubic faces. 
 Ee-entrant angles usually divide the elements of the twins, 
 but these are still better indicated by the optical characters 
 of the mineral. The extinction is always parallel to the 
 diagonal of the cube, as shown by the dotted lines in 
 figs. 21, 22, and 23. The apparent cube appears to be 
 composed of interpenetrating rhombic individuals, whose 
 
THE MATRIX OF THE DIAMOND 
 
 31 
 
 basal pinacoids form the octahedral replacements of the 
 cube. Very frequently four individuals are seen grouped 
 to form a single square, dark lines dividing the deep yellow 
 crystal. The entire cube would then be composed of six 
 individuals. 1 
 
 A second kind of twinning is also common in this 
 perovskite, producing the appearance with crossing nicols 
 of a series of parallel alternately coloured bands, like the 
 poly synthetic twinning in plagioclase felspars. The bands 
 are again often crossed at right angles, as in microcline. 
 These lamellae are parallel to the cubic faces of the com- 
 pound twin. They are alternately pale greenish-blue and 
 pale greenish-yellow, and are all simultaneously extin- 
 guished when they are turned at an angle of 45 to the 
 nicols. The following are among the forms which are seen 
 by the use of this apparatus : 
 
 FIG. 24. Twinned perovskite (crossing nicols) 
 
 It seems, therefore, that a series of rhombic prisms are 
 twinned according to two laws at the same time, the 
 apparent cubo-octahedrons being in reality compound 
 
 1 See Neues Jahrb. 1878, p. 38. 
 
3*2 
 
 THE MATE IX OF THE DIAMOND 
 
 twins. The following, fig. 25, represents diagramrnatically 
 this double twinning. 
 
 op 
 
 FIG. 25. Twinned perovskite 
 
 We have here apparently a polysynthetic or parallel 
 growth, and a simple interpenetrative twinning according 
 to P. The optical peculiarities of perovskite have long been 
 a subject of discussion, and diverse views are at the present 
 time held as to the crystalline system to which it belongs. 
 Some crystallographers l hold that perovskite is a regular 
 mineral, with optical anomalies which are due to strain ; 
 while others 2 believe it to be a rhombic mineral, occurring 
 in compound twins belonging to the class of * mimetic ' 
 minerals. 
 
 The brighter colours of single lamellae, and of certain 
 portions of the compound crystals in the Kimberley rock, 
 suggest that the very weak double refraction exhibited by 
 the crystals, as a whole, may be due to the overlapping of 
 two or more simple components producing a compensation ; 
 a weak double refraction belonging to the untwinned 
 mineral. The re-entrant angles, so common in the 
 Kimberley crystals, seem to have been rarely observed 
 
 1 Klein, Zirkel, Ben Saude. 
 
 2 Descloiseaux, Baumhauer, Groth, Von Koksharow, Tschermak, &c. 
 
THE MATRIX OF THE DIAMOND 33 
 
 in the perovskites of other localities. The striation 
 parallel to the cubical faces, extinguishing when the section 
 is at 45 to the polarisers, occurs also on perovskite from 
 Zermatt, from the Urals (where also all the crystals are 
 penetration -twins), from the Tyrol, from Arkansas, from 
 Wiesenthal (Erzgebirge), &c. The figures of perovskite 
 grains out of the nepheline-hasalt of the last locality, as 
 given by Saner, 1 are very similar to those given above from 
 the Kimberley mineral. 
 
 Perovskite also occurs in the Kimberley peridotite in 
 aggregates of crystals and in irregular grains. Very fre- 
 quently these crystals or grains enclose one or more opaque 
 black octahedral crystals of a titaniferous magnetite (or 
 other spinellid). Often an octahedron or cube of perovskite 
 will have a black grain in the very centre, and when an 
 aggregate of such crystals occurs, each of its components 
 may have a black grain in its centre. 
 
 Fm. 26. Inclusions in perovskite FIG. 27. Titanic iron in perovskite 
 
 This is so common an appearance that one is led to 
 suspect that the perovskite is a secondary mineral, made 
 out of the older titanic iron through some reaction with the 
 basic magma. While, generally, the titanic iron is in the 
 form of small grains in the perovskite, as shown in the 
 above figures, sometimes the perovskite forms a narrow 
 fringe on one side of a larger mass of titanic iron, or makes 
 a shell around it. Sometimes also a crack in a mass of 
 titanic iron is filled with perovskite, as if by a secondary 
 mineral. 
 
 That titanic iron is older than the perovskite is proved 
 by the fact that while titanic iron occurs as an enclosure 
 in the olivine, perovskite never does so. 
 
 1 Zeits. Deuisch. Gcol. Gesell. xxxvii. 1885, p. 447. 
 
34 
 
 THE MATRIX OF THE DIAMOND 
 
 It is very common to find the small perovskite crystals 
 surrounding a large crystal of olivine, as if attracted to it. 
 The following figures are examples of this peculiarity : 
 
 FIG. 28. Perovskite surrounding 
 olivine 
 
 Fio. 29. o, olivine ; r, rntile 
 s, serpentine ; p, perovskite 
 
 The perovskite crystals lie on the outer sides of the 
 olivine crystal, as if a later growth. In the same 
 manner perovskite is attached to the outer surface of 
 serpentine pseudomorphs after olivine. Fig. 29 shows 
 such a case, and shows also in the serpentinised olivine 
 secondary rutile needles growing out of a grain of titanic 
 iron, as already described under olivine. 
 
 A similar grouping of small perovskite crystals, like a 
 wreath, around the olivines has been noticed by Stelzner 1 
 in the melilite-basalt of Hammerer Spitzberg, near Warten- 
 berg, Bohemia (the so-called 'nephelin-pikrit' of Boficky), 2 
 which is rich in perovskite. 
 
 Perovskite is one of the most characteristic minerals for 
 the felspar-free basic eruptive rocks. As a rock ingredient 
 it was first detected by Boficky 3 in the above-named 
 melilite-basalt of Wartenberg. Hussak 4 proved its exist- 
 ence in the nepheline and leucite lavas of the Eifel ; 
 Stelzner 5 showed that it was a constant constituent of 
 melilite-basalts, and Sauer 6 that it occurred very commonly 
 in the nepheline and leucite-basalts of the Erzgebirge. 
 
 1 Neues Jflhrb. Beil. Bd. ii. 1883, p. 415. 
 
 2 Sitzber. der math.-naturw. Classe der bolim. Gesell. Prague, 1876, 
 p. 229. 3 Loc. cit. 
 
 * Sitzber. Akad. Wien, Ixxvii. 1878 (Abth. 1), p. 341. 
 6 Neues Jahrb. Beil. Bd. ii. 1883, p. 396. 
 
 6 Erlauterungen zur geologischen Specialkarte des Kunigreichs Saclisen. 
 Section Kupferberg. Leipzig, 1882, p. 70. 
 
THE MATRIX OF THE DIAMOND 85 
 
 Perovskite has not been identified in a peridotite until 
 quite recently, when my friend, Dr. G. H. Williams, observed 
 it in an eruptive peridotite closely resembling the Kim- 
 berley rock in the State of New York. It has probably 
 been mistaken frequently for other minerals. The 
 colour and form, the similarity to picotite, the included 
 opaque grains, and the mineral associations, all indicate 
 perovskite rather than zircon. Diller 1 has described, as 
 probably aiiatase, certain yellowish, highly-refracting grains 
 occurring around and penetrating ilmenite in an eruptive 
 porphyritic peridotite in Elliott County, Kentucky. Through 
 the courtesy of Mr. Diller and of Prof. A. E. Crandalt, I 
 have received specimens of this interesting rock, and find 
 that these grains are identical with the perovskite of the 
 Kimberley rock. 2 The same form, colour, and enclosures, 
 the same twinning structure, the same high index of re- 
 fraction and low power of double refraction, and the same 
 mineral associations, occur in the Kentucky as in the Kim- 
 berley peridotite. 
 
 It is an interesting fact that, speaking generally, the 
 titanium in acid eruptive rocks takes the form of sphene, 
 in basic non-felspathic rocks of perovskite, and in rocks of 
 intermediate basicity, the felspar-basalts, of ilmenite or 
 titanic iron. An explanation is offered by an important 
 experiment performed by Bourgeois, 3 who was able to form 
 artificial perovskite by fusing its elements with various 
 silicates and basic rocks, and who found that below a certain 
 point of acidity only perovskite was formed, while above 
 that point only sphene was produced. With a titanic 
 spinellid as the primary titanium mineral, the reaction of 
 a basic magma would produce perovskite (as in leucite- 
 and melilite-basalts and in peridotite), while the reaction 
 of an acid magma would produce pphene (as in granite, 
 
 1 Amer. Journ. Sci. xxxii. 1886, p. 124. [Mr. Diller has since withdrawn 
 this opinion.] 
 
 2 For a description of this rock see Section III. 
 
 3 Ann. Phys. Chim. xxix. 1883, p. 481. 
 
 D 2 
 
36 THE MATRIX OF THE DIAMOND 
 
 and trachyte). 1 In both cases the titanic spinellid or 
 ilmenite is surrounded or penetrated by the younger sphene 
 or perovskite, silica being necessary for the formation of 
 sphene out of titanic iron, but not for that of the more basic 
 perovskite. 
 
 ii 
 
 FIG. 30. Perovskite. I, plain ; II, polarised 
 
 The other minerals, which are to be found in examining 
 the specimens from Kimberley, with the exception of the 
 diamond, are less important. 
 
 Magnetite, chromite, titaniferous-magnetitc, and picotite, 
 four isomorphous minerals with difficulty distinguished 
 from one another 2 occur in small grains or crystals scattered 
 through the ground-mass. Chromite is, perhaps, the most 
 abundant of the four, and is primary, while magnetite may 
 in part result from the decomposition of the olivine. The 
 chromite is abundant in minute octahedrons. It is a 
 mineral to be expected in a magnesian rock, occurring in 
 almost all serpentines. Picotite or pleonaste occurs in similar 
 minute grains, the latter of a dark green colour in trans- 
 mitted light. Both the chromite and the spinel-mineral are 
 much smaller than the perovskite crystals. 
 
 Another black mineral in octahedrons occurs in asso- 
 ciation with rutile. Ilmenite proper is, of course, rhom- 
 bohedral, and usually is in thin plates. This mineral may 
 be the same that so often occurs in basalts, and was called 
 ' trapp-eisenerz ' by Breithaupt. In titaniferous magnetite 
 
 1 Sphene also occurs in cla'olite- syenite and phonolite. 
 
 2 For some remarks on this point see Wadsworth, Lithological Studies, 
 section vii. 
 
THE MATRIX OF THE DIAMOND 37 
 
 of this character, in the nepheline-dolerite of Meiches, Knop l 
 found 25 per cent, of titanic iron. 
 
 llmenite is in plates with a purplish metallic glance, as 
 in Rowley Regis basalt ; arid also probably in grains. 
 
 Apatite. In small hexagonal colourless crystals, with a 
 high index of refraction and a low double refraction. The 
 crystals are unusually short, and have a negative character. 
 Sometimes the apatite is faintly pleochroic. It occurs in short 
 crystals in the ground-mass, and also in long actinolite-like 
 crystals, apparently as a contact mineral around enclosures. 
 
 Epidote is in pale yellow grains, with a high index of 
 refraction and a weak yellow pleochroism, and is apparently 
 a secondary mineral due to decomposition. 
 
 Orthite is one of the most interesting of the non-essen- 
 tial minerals. It was noticed in large rounded cleavable 
 grains, as if a primary constituent. It has a chestnut- 
 brown to yellowish-brown colour in transmitted light, and 
 is pleochroic. The pleochroism is more marked than that 
 of epidote, changing from light to dark brown. It has a 
 very high index of refraction, so that its surface appears 
 wrinkled or shagreened. The double refraction is not so 
 high as that of olivine. It has an excellent cleavage parallel 
 to the base, OP, and another parallel to GO Poo . On the 
 basal face or cleavage plane an axis appears in converging 
 light not quite in the centre of the field, and this axis 
 shows a hyperbola coloured green inside and red out- 
 side, as in epidote. 2 The plane of the optic axis is diagonal 
 to the cleavage, and the character is negative. All these 
 characters agree with those of orthite, although this is a 
 new association for that mineral. Orthite occurs in many 
 granitic and hornblendic rocks, as shown by Tornebohm, 3 
 Sjogren, 4 and others, and was found by Vom Rath 5 in 
 
 1 Neues. Jahrb. 1877, p. 696. 
 
 2 Kosenbnsch, Mikrosk. Physiogr. i. 1885, p. 496. 
 
 3 Vega-Exped. Vetensk. lakttagelser, Stockholm, iv. 1887, p. 124. 
 
 4 Stockholm, Geol Foren. ForhandL iii. 1876-77, p. 258. 
 * Zeits. Deutsch. Geol Gesell. xvi. 1864, p. 255. 
 
38 THE MATRIX OF THE DIAMOND 
 
 tonalite, but seems not to have been previously observed in 
 peridotite or serpentine. 
 
 Tourmaline, in strongly pleocliroic short prisms, is a 
 rare but interesting constituent of the rock, being especially 
 abundant around certain inclusions of shale. 1 Itspleochroism 
 changes from brown to light blue. This and other minerals 
 in small quantities are best detected after treating the thin 
 section with hydrochloric acid. 
 
 Sphene, or titanite, was rarely observed, only a few 
 irregular grains being noticed. The finely fibrous form of 
 sphene as a secondary mineral, known as leucoxene, also 
 rarely occurs. 
 
 Tremolite has already been described, also rutile, as 
 secondary minerals. 
 
 Serpentine and serpentinous minerals, as already stated, 
 form a large part of the rock, resulting from the decom- 
 position of olivine. 
 
 Talc. Very minute scales of this mineral were noticed 
 in the ground-mass, and, as a contact or alteration mineral, 
 around certain enclosures. It was highly refracting, had a 
 wavy sheen, high colour, and parallel extinction. 
 
 Calcite is abundantly present in this rock. Diopside 
 can be seen directly altering into this mineral, but the 
 quantity of diopside is so small that we must look else- 
 where for the large mass of calcite that penetrates the 
 rock. It is possible that some readily decomposed lime- 
 bearing mineral, like melilite, originally furnished it ; but it 
 may be that, as Cohen 2 has suggested, the lime has filtered 
 in from without. Calcite is said frequently to form a crust 
 around the diamonds. 
 
 1 It will be remembered that tourmaline is very often a product of con- 
 tact metamorphism in an aluminous rock. T. G. B. 
 
 2 Neues Jahrb. Beil. Bd. v* 1887, p. 195. Cohen here holds, in opposition 
 to Moulle and others, that the ' calc-tuif ' encrusting the ' blue ground ' 
 at the diamond mines is not derived from the diamantiferous ground, but 
 is a later deposit from brackish water during a depression in the Pleistocene 
 Period. 
 
THE MAT1UX OF THE DIAMOND 39 
 
 Zeolites occur in cavities and cracks as a product of 
 infiltration and decomposition. They are very rare in the 
 hard rock here described, but nearer the surface of the 
 mine they occur abundantly in the decomposed blue ground, 
 sometimes forming rock-like masses. The principal zeolite 
 is natrolite. Fibres of natrolite were seen in thin sections 
 radiating inwards, with a more or less tufted arrangement, 
 from the outer edge of a mass of calcite. 
 
 Chalcedony was observed in one instance filling a 
 microscopic cavity in the rock. 
 
 Cyanite. K microscopic mineral occurs in minute 
 quantity in the peridotite, whose exact nature is uncertain, 
 but whose optical characters seem to agree more closely 
 with cyanite than with any other known mineral. It is 
 particularly interesting, as forming usually a zone around 
 enclosures of shale and other rocks, as if a contact mineral. 
 It usually forms a fine compact crystalline zone, but some- 
 times the separate crystals are large enough to be 
 separately studied under the microscope. It occurs in 
 fibrous masses resembling cyanite or actinolite, and has 
 the following properties : a high index of refraction, about 
 equal to that of pyroxene ; the double refraction low, being 
 lower than in actinolite. It is very faintly pleochroic from 
 pale blue to faint green, or, more accurately, pale lavender 
 (corresponding to a) to pale greenish-lavender (correspond- 
 ing to r). The fibrous structure is well marked in this 
 mineral. It has two cleavages, one parallel to the fibres, 
 and one at right angles to them, the latter a 
 often causing a separation, as in apatite. 
 The crystals seem to be brittle, being 
 often broken, as is so common in silli- -> c 
 
 manite. It has a large angle of extinction 
 ( = 32 35). It is unattacked by acid. 
 All these characters seem to be those of 
 cyanite. It would be curious, however, 
 to find cyanite forming contact zones around enclosures 
 in a peridotite. 
 
40 THE MATRIX OF THE DIAMOND 
 
 Diamond. We have deferred to the last the considera- 
 tion of the most interesting mineral in our rock. While 
 the diamond is very difficult to observe in thin sections, it 
 has been found abundantly in the decomposed portion 
 of the peridotite. In practice it is obtained by the fol- 
 lowing process l : The ' blue ground ' is spread out upon 
 the ground and exposed to the sunshine. After a period, 
 dependent on the original condition of the rock, it has 
 crumbled to a coarse powder, and is then placed in rotating 
 washers, and all the lighter material washed away. The 
 residue of chromic and titanic iron, garnet, pyroxene, &c., 
 among which are the diamonds, is then picked over by 
 hand, and the diamonds are separated. The number of 
 diamonds thus obtained is something extraordinary. It is 
 interesting also to find that they become more abundant 
 the deeper they are from the surface, and where also the 
 volcanic action was more intense. They are well crystal- 
 lised in sharp octahedrons, also in dodecahedrons, at times. 
 The crystallography of African diamonds 2 has been de- 
 scribed by several mineralogists, and it is not to our 
 purpose to enter upon that subject. 
 
 Carbonados and black diamonds are also common, not 
 only in large crystals, but very abundantly as minute, 
 almost microscopic, crystals. The abundance of these 
 minute crystals is another proof that they are not 
 enclosures brought up from some other matrix. 
 
 I feel some hesitation in describing certain small highly 
 refracting crystals in the thin sections of the rock, which 
 may possibly be referred to as diamonds. Former at- 
 tempts to describe microscopic diamonds in rock sections 
 have not been successful. Thus, Professor Jeremejew 3 
 
 1 T. Eeunert, Cape of Good Hope Official Handbook, 1886, p. 213. 
 Moulle, ' Memoire sur la geologic generate et sur les mines de diamant 
 de 1'Afrique du Sud,' Ann. des Mines, vii. 1885, p. 193. 
 
 2 Among later papers are Kunz, Proc. Amer. Acad. Sci. and Arts, xxxiv. 
 1886, p. 250. 
 
 3 ' Mikrosk. Diamanteinschliisse im Xanthophyllit der Schischimskisehen 
 Berge des Urals,' Neues Jahrb. 1871, p. 589. 
 
THE MATRIX OF THE DIAMOND 41 
 
 thought he had found microscopic diamonds in xanthophyl- 
 lite from the Urals, the diamonds, in the form of hexa- 
 kistetrahedrons, being held to be very abundant ; but 
 Professor Knop, 1 after a very painstaking and convincing 
 examination, proved the supposed diamonds to be merely 
 holes in the xanthophyllite, the holes being probably 
 negative crystals due to corrosion. By rubbing copper 
 oxide on a dry slide he filled these holes with the black 
 powder. 
 
 Another supposed discovery of diamonds in the matrix 
 was announced by Fouque and Levy, 2 in 1879. They 
 thought that they had observed numerous small diamonds 
 in a thin section of the diabase, the so-called ' ophite 
 andesitique,' which forms overflow sheets in the Karoo 
 shales, and they published photographs of these supposed 
 diamonds in sections. But, as they afterwards found, 3 
 these also were only holes. 
 
 The very minute, isotropic, highly refracting crystals 
 occasionally seen in a thin section of the Kirnberley 
 peridotite are certainly not holes, for they are sometimes 
 of a faint yellowish, or, more frequently, bluish colour, and 
 are often entirely embedded in the ground-mass. They 
 never occur as enclosures in other minerals, but, like 
 the perovskite, lie scattered in the ground-mass only ; 
 belonging, therefore, to a later T n ni 
 
 generation of minerals than 
 the olivine and bronzite. 
 They are always in the form 
 
 J . . FIG. S3. Minute diamonds 
 
 of entire crystals, even m 
 
 the thinnest slide, as if they were too hard to be cut. The 
 
 shape is that of an octahedron with rounded faces ; tri- 
 
 1 ' Ueber die Bedeutung der fiir Diamant gehaltenen Einschliisse im 
 Xanthophyllit der Schischimskischen Berge des Urals,' Neues Jahrb. 1872, 
 p. 785. 
 
 2 ' Note sur les Roches accompagnant et contenant le diamant dans 
 1'Afrique Australe,' Bull. Soc> Min. de France, ii. 1879, p. 216. 
 
 3 Neues Jahrb. i. 1881, p.. 194. 
 
42 
 
 THE MATRIX OF THE DIAMOND 
 
 angular facets are also seen. (In some cases larger holes of 
 the same octahedral shape may be observed in the section, 
 as though a crystal had dropped out during the process of 
 grinding.) Frequently these bodies seem to have concave 
 faces, viz., as in fig. 32, ii. and iii. ; this, however, is probably 
 only an optical illusion. They sometimes have a decided 
 yellow colour. They have a high index of refraction, and a 
 dark rim around them. They are usually isotropic, but 
 traces of weak double refraction in the centre of one of the 
 crystals have been seen, a pale bluish colour appearing in 
 certain positions, as if it were a crystal under strain. I 
 
 . took some of the same rock from 
 which the section was made, and 
 after pulverizing it, separated 
 the heaviest portion by means 
 of Thoulet's solution. This was 
 put upon a glass plate with a few 
 drops of water, and then rubbed 
 with a polished sapphire. The 
 sapphire was clearly scratched. 
 A photograph of one of these 
 bodies (fig. 33) was taken by a 
 friend, the supposed diamond 
 lying between three crystals of titanic iron. Four of these 
 supposed diamonds were seen in a single section of the 
 rock. 
 
 I am not, however, prepared to state that these bodies 
 are diamonds, not having been able to isolate them. 
 Several colourless isotropic minerals appear in the rock, 
 among which a colourless garnet, probably dernantoid, 
 occurs in small crystals and might readily be supposed to 
 be a diamond. 
 
 Mr. Hedley, of the Colonial Exhibition, from whom I 
 obtained my specimens, informed me that diamonds have 
 been found in the rock as well as in the soft decomposed 
 material ; but as yet their detection under the microscope 
 cannot be said to be free from doubt. . 
 
 FIG. 33. Microscopic section of the 
 Kimberley peridotite, f, ilmenite ; 
 t, titanic iron ; d, diamond (?) 
 
THE MATRIX OF THE DIAMOND 43 
 
 The larger diamonds from Kimberley have been the 
 subject of study by several investigators. They have been 
 found sometimes to have optical anomalies due to strain, 
 so that they are not perfectly isotropic. Eizeau thought 
 this strain to have been caused by the unequal distribution 
 of heat during rapid cooling ; but Jannettaz 1 holds that 
 the strain is due to compressed gas in the interior of the 
 crystal. The latter theory seems to be supported by the 
 fact that the diamonds frequently crack or fly to pieces 
 after having been taken from the mine. It is a pheno- 
 menon perhaps similar to that which occurs with the 
 smoky quartz of B ranch ville, Connecticut, which, as 
 Wright 2 has proved, is tilled with liquid carbonic acid, and 
 flies to pieces with a report when struck, as so well 
 described by Hawes. 3 The fact that fragments of the 
 diamonds are often found separated in the mine has been 
 used as an argument that the blue ground is not a volcanic 
 rock but an aqueous mud derived from one. This argu- 
 ment falls to the ground on our knowing that the separation 
 of these fragments is not due to a flow of the matrix, but to 
 the bursting of the diamonds themselves on exposure to 
 the atmosphere. 
 
 The Kimberley diamonds contain various enclosures, 4 
 among which hematite is the most abundant. Zirkel, 5 
 before the discovery of the South African diamond mines, 
 gave a full resume of the inclusions in diamonds. Schrauf 6 
 has described a curious case of one diamond enclosed in 
 another, a fact formerly mentioned by Kenngott. 7 The 
 researches of Harting 8 upon inclusions in diamonds, as 
 
 1 ' Sur les colorations du diamant dans la lumiere polarisee,' Bull. Soc t 
 Min. de France, ii. 1879, p. 124. 
 
 Amer. Jmirn. Sci. xxi. 1881, p. 209. 3 Ibid. p. 203. 
 
 Cohen, Neues Jahrb. 1876, p. 752. 
 
 Zirkel, Mikrosk. Beschaff. der Min. 1873, p. 250 (gives literature). 
 
 Tscherinak, Min. Mitth. 1873, p. 289. 
 
 Wien. Akad, Sitzber. x. 1853, p. 182. 
 
 Verhdl. d. Kon* Instit. van Wetensch., Lettcrkunde <&c. te Amsterdam, 
 vi. 1858, 
 
44 THE MATRIX OF THE DIAMOND 
 
 well as those of Brewster, Petzhold, Wohler and Desclois- 
 eaux, Sorby and Butler, Damour and Dumas can only 
 here be mentioned. The supposed discovery by Goeppert 1 
 of plants and organic cells in the diamond has not yet been 
 verified. 
 
 The explorations of the last few years have placed it 
 beyond question that the serpentine rock called 'blue 
 ground' is in reality the matrix of the diamond. For a 
 time it was thought that the diamonds were washed into 
 the ' kopjes ' from above, being mere alluvial deposits, as 
 held by Mr. Cooper 2 and others ; afterwards, and until the 
 present time, the idea has been general that they were 
 carried up from below along with other inclusions, and 
 that their true matrix was some gneiss or itacolumite far 
 below, from which they had become detached by volcanic 
 agency. Others again, such as Doll, 3 hold that while the 
 serpenlinous rock is the matrix of the diamond, the latter is 
 a secondary mineral due to the decomposition of the rock. 
 
 But recent investigations seem to place it beyond ques- 
 tion that diamonds are as much a part of the Kimberley 
 rock as biotite, garnet, titanic and chromic iron and perovs- 
 kite, and that, like these minerals, they may be considered as 
 a rock ingredient. The fact that they continue just as abun- 
 dant, if not more so, the deeper the mines are explored : 
 that they are never found in, or especially associated with, 
 the foreign inclusions of gneiss, granite, or sandstone : that 
 they are distributed abundantly through all parts of the 
 rock : and that in each of the four principal mines the 
 diamonds have distinctive features of colour, lustre, and 
 shape, are, with the microscopical evidence of the eruptive 
 
 1 ' Ueber algenartige Einschliisse in Diamanten,' Breslau. Abhandl. der 
 schles. Gesell. fur vaterlandische Cultur, Abth. fur Naturwissenschaften 
 und Medicin, 1868-69, p. 61. He describes supposed algse enclosed in 
 diamonds, comparing them with Eozoon and Oldhamia, and names them 
 ' Protococcus adamantinus ' and ' Palmogloeites adamantinus.' 
 
 2 Cooper, Proc. GeoL Assoc. iii. 1874, p. 336. 
 
 3 VerJuindl. gcol Reichsanstalt, 1880, p. 78. 
 
THE MATRIX OF THE DIAMOND 45 
 
 character of the rock, strong reasons for holding that the 
 diamonds now lie in their original matrix. 
 
 Ground-mass. All the above-described minerals lie, 
 some of them porphyrifcically, in a ground-mass or base, 
 which we may now examine. This is a more or less 
 homogeneous serpentinous mass, which, by reason of the 
 decomposition it has suffered, is very difficult to study. 
 It is now mainly composed of a nearly isotropic serpentinous 
 mineral mixed with calcite. By treating the slide with hot 
 hydrochloric acid, the iron and calcite are dissolved away 
 and the amorphous and more readily soluble portions of 
 the ground-mass eliminated, so that traces of the original 
 structure for the first time become visible. Forms of small 
 prismatic crystals (possibly a pyroxenic mineral) can now 
 be seen occasionally, and between them are traces of an 
 isotropic substance which may indicate a non-crystalline 
 base. Certain resemblances can be traced to the ground- 
 mass of sundry decomposed basaltic or other basal rocks. 
 The base now, however, is a greenish serpentinous substance 
 full of calcite grains, flour-like grains of gibbsite, rounded 
 dusty masses of ferruginous and kaolinic material, &c., the 
 original structure being entirely lost through disintegration. 
 Until fresher specimens are obtained it is impossible to speak 
 with any confidence concerning the original structure of the 
 ground-mass. In one case already mentioned, a brown glass 
 was noticed enclosed in olivine. Any similar basic glass in 
 the ground-mass has long since been entirely decomposed. 
 
 Fragmented Enclosures. Fragments, both of the adjoin- 
 ing shale and diabase, and also of more deeply seated 
 granite, gneiss, eclogite and other rocks, occur in the 
 Kimberley peridotite. Those of shale are by far the most 
 numerous, sometimes becoming so abundant as to form 
 the greater portion of the rock. 1 A breccia of shale 
 
 1 Nevertheless in a large specimen, given to me by Sir J. B. Stone, I 
 could not with certainty identify any shale, even under the microscope, but 
 fragments of a compact rock of peculiar structure were present. See GeoL 
 Mag. 1895, p. 498. (It is represented on Plate I. T. G. B.) 
 
46 THE MATRIX OF THE DIAMOND 
 
 cemented by the serpentinous rock may then occur. The 
 adjoining shale in place is a black bituminous rock full of 
 pyrite, burning when set on fire. When kept, both un- 
 burned and burned specimens after a time become covered 
 with alum. The fragments of shale in the peridotite are 
 more compact and have lost their shaly character, their 
 bituminous or carbonaceous matter and their sulphur. 
 The microscope shows that they have also frequently been 
 mineralogically altered by the heat of the lava ; having 
 lost the character of a shale and become filled with aggre- 
 gates of micaceous minerals. Often the shale fragment is 
 corroded away to a skeleton or shell, filled with the ground- 
 mass (fig. 34). In another case a zone of grey kaolin-like 
 
 FIG. 34. Shale fragment filled with the Fio. 35. Shale fragment surrounded 
 
 ground-mass by calcite 
 
 substance occurred around the fragment, while calcite was 
 outside of all (fig. 35). 
 
 These enclosures occur of all sizes, from fine powder to 
 very large masses. The largest masses are seen only at 
 the top of the mine, and are made of shale ; they are 
 called ' floating reef.' In regard also to smaller frag- 
 ments, shale is most abundant at the top of the mine, and 
 less abundant the deeper we penetrate. Bounded fragments 
 of granite, mica- schist, and quartzite are found, though 
 rarely, and fragments of diabase also occur. All seem to 
 have been carried upwards. 
 
 Chemical Composition of the Ground-mass. Almost all of 
 the rock is soluble in acid, a small residue of garnets, 
 biotite, bronzite, perovskite, ilmenite, chromite, &c., re- 
 maining. By repeated treatment with hydrofluoric and 
 
THE MATEIX OF THE DIAMOND 
 
 47 
 
 sulphuric acid all the silicates except garnet are dissolved, 
 which with perovskite forms the larger part of the residue. 
 
 The specific gravity of the rock was determined by the 
 use of Klein's cadmium solution and Westphal's balance, 
 and is somewhat less than the true specific gravity. 
 
 Two varieties were analysed 1 : 
 
 I. The least decomposed rock, with few shale enclosures. 
 
 II. The more decomposed rock, with many shale 
 enclosures (diamantiferous). 
 
 Si0 2 (with some Ti0 2 ) 
 
 FeO (including A1 2 3 ) . . 
 
 MgO .... -. 
 
 CaO . . . . . 
 
 Na,0 . ,-."... 
 
 C0 2 . 
 
 H 2 (carbonaceous matter, &c.) 
 
 Spec. grav. 
 
 I. 
 
 n. 
 
 33-00 
 
 34-80 
 
 12-00 
 
 14-40 
 
 32-38 
 
 30-76 
 
 9-60 
 
 2-70 
 
 0-67 
 
 1-40 
 
 7-05 
 
 5-55 
 
 6-00 
 
 10-60 
 
 100-70 
 
 100-21 
 
 2-734 
 
 2-64-2-70 
 
 Since, in 
 the 7-05 C0 2 , 
 
 Analysis 
 we get : 
 
 1.8 
 
 97 
 
 of the CaO clearly belongs to 
 or, eliminating the calcite : 
 
 
 
 
 
 in. 
 
 IV. 
 
 Si0 2 , &c. 
 FeO, &c. 
 
 33-00 
 12-00 
 
 Si0 2 , 
 FeO, 
 
 &c, 
 &c. 
 
 . 39- 
 . 14- 
 
 25 
 
 27 
 
 MgO 
 CaO 
 
 
 
 
 
 
 
 32- 
 
 
 38 
 63 
 
 MgO 
 CaO 
 
 
 
 . 38- 
 
 o- 
 
 51 
 
 75 
 
 Na 2 
 CaCO 
 H 2 0, 
 
 3 (calcite) 
 &c. 
 
 
 16- 
 6- 
 
 67 
 02 
 00 
 
 Na 2 
 H 2 0, 
 
 &c. 
 
 , o- 
 
 7- 
 
 79 
 13 
 
 100 
 
 70 
 
 100- 
 
 70 
 
 1 The titanic acid (at least 1 per cent.) was not separated from the 
 silica, nor the alumina (which was in small quantity in Analysis I.) from 
 the iron. The CO 2 was estimated directly in a C0 2 apparatus, using dilute 
 acid. The carbonaceous (organic) matter and moisture were determined by 
 ignition over a blast lamp, and from the total loss deducting the C(X already 
 determined and correcting for the gain of oxygen by the FeO. 
 
48 THE MATRIX OF THE DIAMOND 
 
 From Analysis IV. the amount of serpentine in the 
 rock can he readily calculated. A typical serpentine l has 
 the composition of 
 
 Si0 2 MgO H 2 
 43-48 43-48 13-04, 
 
 the water being T 2 of the whole. In the Kimberley rock 
 freed from calcite the water is only -fa of the whole, so that 
 we may conclude that about half of the rock is serpentine. 
 The analysis shows that olivine forms the principal con- 
 stituent of the remaining portion of the rock. The slight 
 excess of silica beyond that required to form olivine, 2 
 
 (39*12 18-16 
 
 garnet present in small proportions. 
 
 The calcite, forming 16 per cent, of the rock, is probably, 
 with most of the serpentine, the result of the decomposition 
 of the ground-mass. Unless we assume that the lime is 
 derived from without, which would be difficult to explain, 3 
 it has come from the decomposition of certain lime-bearing 
 minerals. With the exception of chrome-diopside which 
 is present only in small quantity the porphyritic crystals 
 are practically free from lime. It may have come from 
 diopside, melilite, or some other lime-bearing mineral in 
 the ground-mass. The small percentage of alumina and the 
 mineral associations exclude felspar as a constituent. 4 Calcite 
 frequently occurs in serpentine, and is generally regarded 
 as the result of the decomposition of a pyroxenic mineral. 5 
 
 1 Kammelsberg, Zeits. Deutsch. Geol. GeselL xxi. 1869, p. 97 ; Mineral. 
 Chemie, Leipzig, Theil ii. 1875, p. 506. 
 
 2 Stelzner, ' Ueber den Olivin des Melilithbasaltes vom Hochbohl,' 
 Neues Jahrb. i. 1884, p. 271. 
 
 3 Surely not ; because, where volcanic action has been, springs with 
 CaCO 3 are common. T. G. B. 
 
 4 It would equally exclude nepheline. T. G. B. 
 
 5 Doelter, Ueber das Mutter g estein der bohmischen Pyropen ; Tschermak, 
 Min. Mitth. 1873, p. 13, and other references. 
 
 (It is so sometimes, but it is often infiltrated from without, as in the so- 
 called ophicalcite formed from brecciated serpentine. T. G. B.) 
 
THE MATRIX OF THE DIAMOND 49 
 
 The extreme basicity of the rock, the abundance of the 
 calcite as a decomposition product, the high magnesia and 
 low alkali, the presence of biotite, and more especially of 
 perovskite, point to the possible presence of nepheline or 
 melilite in the ground-mass. All these characters occur in 
 melilite-basalt. 1 Traces of a mineral giving rectangular 
 sections occur in the ground-mass, which possibly are to be 
 referred to melilite or nepheline, but its altered state pre- 
 vents this suggestion from being confirmed with the present 
 material. Tn melilite-basalt, as in the Kimberley rock, the 
 pyroxene is chrome-bearing, the perovskites surround 
 the olivine ' einsprenglinge,' garnets may occur, and the 
 augite may be replaced 2 by biotite. 3 
 
 The composition of the whole rock, characterised by a 
 low amount of silica and a high amount of magnesia, 
 together with much lime and little alkalies, may be com- 
 pared with that of certain garnetiferous olivine serpentines. 4 
 Among unaltered rocks the only ones that show similar rela- 
 tions between the silica and magnesia are dunite, 5 olivinfels, 6 
 
 1 Stelzner, ' Ueber Melilith und Melilithbasalte,' Neues ~Jahrb. Beil. 
 Bd. ii. 1883, p. 369. 
 
 - Tornebohm, ' Melilitbasalt frSn Alno, Stockholm,' Geol. Fb'ren. For- 
 handl. vi., 1882-83, p. 240. 
 
 3 Professor Eosenbusch, to whom these proofs have been submitted, re- 
 marks that it would have been a great satisfaction to Prof. Carvill Lewis 
 if he had lived to know that in the State of New York dykes of Alnoite are 
 now known to exist in the vicinity of dykes of the Kimberlite character. 
 T. G. B. 
 
 4 Compare serpentine from Zoblitz (Lemberg, Zeits. Deutsch. Geol. 
 Gesell. xxvii. 1875, p. 532) with the following composition : 
 
 Si0 2 Fe 2 3 + ALjOj MgO CaO H.,O 
 
 39-27 8-98 38-78 1-16 11-81 
 
 Compare, also, analyses of many serpentines quoted in Wadsworth, Litho- 
 logical Studies, 1884, table 4. 
 
 5 Dunite from the Vosges (Tschermak, Min. Mitth. 1875, p. 187) ; New 
 Zealand (Zeits. Deutsch. Geol. Gesell. xvi. 1864, p. 341) ; North Carolina 
 (Amer. Journ. Sci. xxxiii. 1862, p. 199), <fec. 
 
 6 Olivinfels from Steiermark (Tschermak, Min. Milth. 1872, p. 79) ; from 
 Norway (Ejerulf, Verhandl. Geol. Reichsanstalt, 1807, p. 71), &c. 
 
 E 
 
50 THE MATRIX OF THE DIAMOND 
 
 and chassignite l (an olivine meteorite) . The structure 
 of the Kimberley rock, as will presently be shown, differen- 
 tiates it from these, which are all holocrystalline. The 
 rock now described appears to differ from any hereto- 
 fore known. Picrite-porphyrite is practically a felspar-free 
 melaphyre, or, perhaps in deference to its hornblende, it 
 may be called the effusive form of the rock named camp- 
 tonite by Kosenbusch. Picrite-porphyrite is also an augitic 
 rock, and contains less magnesia than the Kimberley rock. 
 Limburgite, the neovolcanic equivalent of picrite-porphyrite, 
 is likewise an essentially augitic rock, being a non-felspathic 
 basalt, 2 and is also much poorer than the Kimberley rock. 
 
 There appears to be no named rock-type having at once 
 the composition and structure of the Kimberley rock. For 
 this reason, as also on account of its importance as the 
 matrix of the diamond, it is now proposed to name the 
 rock Kimberlite. 
 
 Kimberlite may be described as a porphyrific volcanic 
 peridotite of basaltic structure, or, according to Kosen- 
 busch's nomenclature, the palseovolcanic ' ergussform ' of a 
 biotite-bronzite-dunite, being an olivine-bronzite-picrite- 
 porphyrite rich in biotite. Had it less olivine and more 
 rhombic pyroxene it could be classed among the picrite- 
 porphy rites, and be called a saxonite-porphyrite. As it is, 
 it is more nearly related to a dunite-porphyrite. Prof. 
 Judd has described a porphyritic dunite, but that is a holo- 
 crystalline deep-seated rock of entirely different structure 
 from the rock under consideration. In fact Kimberlite is a 
 rock sui generis, dissimilar to any other known species. 
 
 Three varieties of Kimberlite may be distinguished : 
 
 1 Vauquelin (Ann. Pliys. Chim. i. 1816, p. 49) ; Damour (Paris, Comptes 
 Rendus, Iv. 1862, p. 591) ; Tschermak (Wien. Akad. Sitzber. Ixxxviii. 1883 
 (Abth. i.), p. 361). 
 
 a This must be understood in the sense that felspar has not yet separated 
 from the glassy basis. From the chemical composition of the rock, it is 
 reasonable to conclude that limburgite, with a different environment, would 
 appear in the form of a picrite ; i.e. a rock containing some felspar, but not 
 so much as in a dolerite. T. G. B. 
 
THE MATRIX OF THE DIAMOND 51 
 
 (1) Kimberlite proper, a typical porphyritic lava ; (2) Kimbcr- 
 lite breccia, the same lava broken and crushed by volcanic 
 movements and crowded with included fragments of shale ; 
 (3) Kimberlite tuff, being the fragmental and tufaceous 
 portion of the same volcanic rock. These varieties pass 
 by insensible gradations one into another, so that no 
 sharp line can be drawn between them, and all occur 
 together in the same neck or crater. The Kimberlite 
 breccia forms by far the greater portion of the rock, and is 
 rich in diamonds. It is traversed by dykes of Kimberlite 
 proper, and contains streaks and patches of softer ' soapy ' 
 material, which appears to be the Kimberlite tuff. The 
 deeper portions of the Kimberlite breccia become more 
 compact as though passing gradually into Kimberlite proper. 
 The so-called 'blue ground' has also been analysed, 
 but being so thoroughly altered, the analyses are of small 
 scientific value. 
 
 Perhaps the most interesting chemical observation con- 
 cerning this 'blue ground' was that made by Sir H. E. 
 Koscoe. He found l that on treating it with hot water an 
 aromatic hydrocarbon could be extracted. By digesting 
 the ' blue ground ' with ether, and allowing the solution 
 to evaporate, this hydrocarbon was separated and found to 
 be crystalline, strongly aromatic, volatile, burning with a 
 smoky flame, and melting at 50C. 
 
 Structure. The structure of Kimberlite, to which sub- 
 ject we may now proceed, is its distinguishing and charac- 
 teristic feature, differentiating it from ordinary serpentines 
 and peridotites, if not from all other terrestrial rocks. The 
 structure can only be compared with that of certain 
 meteorites. 
 
 It may be described as a porphyritic brecciated struc- 
 ture. While evidently the structure of an eruptive rock, 
 it at the same time shows clear proof of mechanical disturb- 
 ances during or after its cooling. According as the por- 
 
 Manchester, Lit. Phil. Soc. Proc. xxiv. 1885, p. 5. 
 
52 THE MATRIX OF THE DIAMOND 
 
 phyritic or the brecciated structure happens to predominate 
 in the section under examination, the observer varies in 
 his opinion as to whether the rock is a lava or a tuff. 
 
 Cohen, Hudleston, Moulle, and others, believed it to be 
 an igneous tuff, while Dunn, and Maskelyne and Flight con- 
 sidered it to be an eruptive gabbro-like rock. 
 
 When comparatively free from enclosures the porphyritic 
 structure may be as distinctly shown as in a basalt. 
 The greater mass of the porphyritic crystals (the ' einspreng- 
 linge ') are the olivines, which often have distinct crystalline 
 form. These are, as already stated, more frequently 
 rounded and like the olivines in basalts, and may show the 
 action of a corrosive magma. Biotite, bronzite, garnet and 
 other substances also form comparatively large crystals, 
 usually rounded, and, with the olivines, lie separately in a 
 more or less isotropic ground- mass made mainly of a serpen- 
 tinous mineral. The rock therefore is not holocrystalline, 
 but belongs to the class of volcanic or effusive rocks 
 (' erguss-gesteine'), characterised by idiomorphic porphyritic 
 crystals floating in a ground-mass. 
 
 That the rock was a true igneous lava, and not a mud 
 or ash, is indicated by the following facts : 
 
 1. The minerals and their associations are those character- 
 
 istic of eruptive ultra-basic rocks. 
 
 2. The porphyritic crystals are idiomorphic as in volcanic 
 
 rocks. 
 
 8. The corrosion cavities (' einbuchtungen ' ) in the por- 
 phyritic crystals are due to solution by the hot magma. 
 
 4. The character of the bronzite and diopside is similar 
 
 to that in meteorites and eruptive rocks, but not in 
 metamorpbic or plu tonic rocks-. 
 
 5. The occurrence of a ground-mass and of traces of glass. 
 
 6. The traces of a second generation of minerals (pyroxene ?) 
 
 in the ground-mass. 
 
 7. The occurrence of fragmentary enclosures of the adjoining 
 
 rock and of deep-seated rocks, and the evidence of 
 alteration by heat which these enclosures exhibit. 
 
THE MATRIX OF THE DIAMOND 53 
 
 8. The traces of a fluidal structure shown on polished 
 
 specimens. 
 
 9. The identity of the rock with one in Kentucky, which is a 
 
 true eruptive dyke, and with others in the Vaal River, 
 which also form dykes. 
 
 That it is not a tuff is shown by the entire absence of 
 stratification, of clayey or ashy bands, of water-worn frag- 
 ments, of cementing material, and by its geological position : 
 not as an overflow mud deposit, but in the very neck of a 
 volcano. 1 
 
 The brecciated structure of the rock is shown not only 
 in the abundance of angular fragments of shale it contains, 
 but also in the broken and angular character of many of 
 the porphyritic crystals in it, and the mechanical manner in 
 which they seem to have been sometimes pushed together. 
 
 Yet the structure is not a purely mechanical one, such 
 as is the case with certain ancient rocks -which have been 
 subjected to heavy pressure. A so-called mechanical-por- 
 phyritic structure is well known in deep-seated peridotites, 2 
 being particularly well marked in the variety named olivin- 
 fels. These, as Brogger 3 and Reusch have shown in Nor- 
 way, are often so crushed as to resemble a sandstone. 
 Here, however, under the microscope the so-called ' cata- 
 clastic ' structure, 4 or 'mortel-structur,' 5 whereby the 
 outer portions of the crystals are smashed into a mosaic- 
 like band (as in 'augengneiss,' &c.) can always be seen. No 
 traces of this cataclastic structure occur in the Kimberley 
 peridotite. The olivines have no mosaic borders or ends, no 
 ' eyes ' of them are made, and their rounded form is certainly 
 
 1 (But suppose the rock were an agglomerate ? This appears to me 
 equally consistent with all the reasons given above, except, perhaps, 8 and 
 9, of which the former is very dubious, but the latter no doubt is weighty, 
 because an agglomerate does not usually have a dyke-like habit. T. G. BJ) 
 
 - Rosenbusch, Mikrosk. Physiogr* ii. 1887, p. 273 
 
 3 Neues Jahrb. 1880, ii. p. 187. 
 
 4 Kjerulf, Christiania, Nyt. Mag. Naturvid. xxk. 1885, p. 215. 
 
 * Tornebohn, Stockholm, Gcol. Foren* ForhandL v. 1880-81, p. 233. 
 
54 THE MAT BIX OF THE DIAMOND 
 
 not due to pressure. The brecciated structure, therefore, 
 whatever its cause, is not due to pressure. 
 
 Several causes may produce brecciation in a volcanic 
 rock. It may be due : 1. To the rapid cooling and consequent 
 shrinking and cracking of a fluid lava ; 2. To the contact of 
 the moving lava with the adjoining rock which is carried 
 along with it and broken up to form a so-called friction 
 breccia ('reibungsbreccia'); 3. To subsequent explosions and 
 movements in the crater of the volcano. It is quite possible 
 that in the present instance all three of these causes may 
 have operated. 
 
 As to the first cause, the words of Dr. Wadsworth, 1 if 
 applicable, seem prophetic. After explaining the brecciated 
 character of meteorites as due to rapid crystallisation, he 
 says : ' If we could find rapidly cooled, unaltered terrestrial 
 peridotic rocks, I should expect to find in them the chon- 
 dritic structure, -the same as the Estherville meteorite 
 possesses the structure of an unaltered terrestrial peridotite, 
 and the meteoric pallasites possess that of the terrestrial 
 ones.' Roth 2 speaks of the formation of lavas and slags 
 which fall apart on cooling. 
 
 The second process, which causes a ' friction breccia,' 
 is well known in many volcanic districts. It is seen on 
 approaching the vent of the volcano. Naumann 3 has given 
 some excellent examples of this in Saxony, where in the 
 border between porphyry and shales, great masses of the 
 breccia, the so-called ' Brockengesteine ' is formed, and the 
 mass of the enclosed slates may predominate over the mass 
 of the porphyry. 
 
 The third process, the result of successive explosions in 
 the same crater, is also common in volcanic districts. In 
 this case, not only are fragments of the adjoining rock en- 
 closed in the lava, but the older and hardened magma 
 itself is broken up and imbedded afresh in the new erup- 
 
 1 Lithological Studies, 1884, p. 111. 
 
 2 Allg. und chem. Geol. Berlin, ii. 1883, p. 207. 
 
 3 Lehrtyich der Geognosie, Leipzig, i. 1858, p. 917. 
 
THE MATRIX OF THE DIAMOND 55 
 
 tion. In this case the old lava forms the larger part of the 
 breccia, and the final composition and structure is not un- 
 like that of a tuff. It is of course just this material which, 
 when ejected in the form of dust or mud, does make the 
 stratified ashes called tuff. This kind of breccia occurs in 
 the Euganean Hills, 1 in Italy, 2 and perhaps in Wales. 3 
 
 According to Chaper, 4 who has studied the geology 
 of the Kimberley mines, the eruption has taken place at 
 many successive periods ; all his observations pointing 
 to a series of eruptions, between each of which there 
 was time for the volcanic mass to consolidate. He says 
 that the great irregularities so puzzling to the miners are 
 thus explained, and that at Bulfontein and Du Toits Pan 
 it is possible to make out a chronology of the various 
 eruptions. 
 
 If this last is the principal cause of the breccia it is 
 no wonder that the rock should so closely resemble a tuff. 
 It is, of course, difficult to draw the line between a brecciated 
 lava and a tuff, but in this instance everything points to 
 its lava-like character. The tuff would lie outside of the 
 volcano, the brecciated lava in its vent. The conception 
 of a true porphyritic lava, afterwards broken by paroxysmal 
 eruptions, seems perfectly to explain the nature of the 
 remarkable rock which is now under discussion. Certain 
 so-called ' soapy ' bands in the mine probably represent the 
 true tuff. Just as the limburgite of the Kaiserstuhl district 
 alternates with beds of tuff, so here it is probable that 
 
 1 Keyer, Fisik der Eruptive ; Die Euganaen. [It is often very well 
 exhibited in the dykes of basalt cutting through lower carboniferous rocks 
 near Burntisland, Scotland. See, for other cases, Proc. Geol. Assoc. vii. 
 No. 2.-T. G. B.] 
 
 2 The piperno. 
 
 3 Bonney, Quart. Journ. Geol. Soc. xxxv. 1879, p. 311. [It may also 
 be produced by more solid parts of the lava being ruptured and swept along 
 by the onward pressure of the more liquid mass, the result being often 
 called a fluxion-breccia. T. G. B.] 
 
 4 Bull. Soc. Min. de France, ii. 1879, p. 195. ' Sur les mines de diamant 
 de 1'Afrique Australe.' 
 
56 THE MATRIX OF THE DIAMOND 
 
 Kimberlite tuff occurs together with the Kimberlite 
 breccia. 
 
 A comparison of the Kimberlite with known ashes or 
 tuffs, Professor Kosenbusch having kindly placed his 
 collection at my service for this purpose, has failed to 
 establish any analogy with them, and I am compelled 
 to differ from Professor Cohen and others who speak of 
 it as ash, mud, or conglomerate, and to regard it as a true 
 eruptive lava. 
 
 The structure of the African Kimberlite is equally 
 shown in the Kimberlite from Elliott County, Kentucky, 
 and with that from Syracuse, New York. I have compared 
 the Kentucky rock with the African rock directly. Dr. 
 Williams has published a photograph of that from Syra- 
 cuse. 1 In mineral composition, in eruptive character, in 
 structure, in enclosures, the three rocks are identical. As 
 the Kimberlite of Kentucky and New York State occurs in 
 dykes, not volcanic vents, it becomes all the more certain 
 that the porphyritic structure is an original one characteristic 
 of the rock. 
 
 Although, as already stated, the peculiar character of 
 Kimberlite is shared by no other terrestrial rock, it is 
 of high interest to find that in structure it resembles 
 meteorites of similar composition. Attention has already 
 been called to the likeness of some of its minerals to 
 those in meteorites, and its chemical composition has also 
 been shown to be closely related to that of the olivine 
 meteorite called chassignite. 
 
 If we were to replace the ground-mass of Kimberlite by 
 native iron, we should get a rock nearly allied in both struc- 
 ture and composition with the well-known class of meteorites 
 known under the name of chondrites. These meteorites 
 are both porphyritic and brecciated, and when the breccia 
 structure is well developed it has given rise to the same 
 
 1 For notes upon specimens afterwards obtained from these localities by 
 Professor Lewis, see Section IIL 
 
THE MATRIX OF THE DIAMOND 57 
 
 discussion as Kimberlite, as to whether they are tuffs or 
 lavas. Haidinger was one of the first to describe the 
 so-called meteorite-breccias, and to show that not only are 
 angular fragments of other rocks frequently enclosed in the 
 olivine rock, but that the meteoric rock itself is often 
 broken into angular and rounded fragments cemented 
 together, as if a volcanic tuff. Tschermak l holds to the 
 tuff-like character of certain meteorites, yet remarks that 
 ' There occur passages into the tuff structure, so that the 
 same stone may be designated by one observer as crystalline, 
 by another as clastic.' Another structure in these olivine 
 meteorites is the occurrence of rounded masses of olivine 
 or of olivine and enstatite, called the chondritic structure. 
 The origin of this has given rise to much discussion. A 
 chondrus may consist of a single optically continuous mass 
 of olivine, or it may be polysomatic, that is, due to a number 
 of individuals. 
 
 Polysomatic chondri of olivine occur in the Kentucky 
 Kimberlite. The olivines are laid together, as if in a 
 mosaic, the whole forming an irregular sphere. This 
 is identical with a granular chondrus in a meteorite 
 from Seres figured by Tschermak. 2 Glass which occurs in 
 these chondri occurs also in a chondrus from Kimberley. 
 
 1 Die mikrosk. Beschaff. der Meteoriten, Stuttgart, 1885, p. 3. 
 
 2 Ibid. (Plate VIII. fig. 2.) 
 
58 
 
 SECTION III 
 
 KIMBERLITE FEOM THE UNITED STATES 
 BY PROFESSOK T. G. BONNEY 
 
 Two rocks from the United States, specimens of which were 
 in Professor Carvill Lewis' collection at the time of his death, 
 present, as will be seen hereafter, a very close macroscopic 
 and microscopic resemblance to the diamond-bearing rock 
 from South Africa. One occurs at Syracuse, New York ; 
 the other about six miles south-west of Willard, in Elliott 
 County, Kentucky. For the most recent information relat- 
 ing to the former rock we are indebted to the late Professor 
 G. H. Williams ; the latter has been described by Mr. 
 J. S. Diller. 
 
 1. Rock of Syracuse, New York. 1 There are two types 
 of this rock, according to Professor G. H. Williams ; one of 
 these is a very dark green, almost black, rock, with minute 
 specks of glistening mica, occasional larger plates of a brass- 
 yellow mineral (4x6 mm.), and a few small masses of a 
 lighter green more compact serpentine with a sharp crystal 
 form. The other is paler in colour, composed of a dense 
 
 1 Literature. G. H. Williams, Science, March 11, 1887 ; Amer. Journ. 
 Sci. xxxiv. 1887, 137 ; Bull. Geol. Soc. Amer. i. 1890, p. 533. He cites 
 Vanuxem (Third Annual Report, 1839, and Final Report on Geol. of Third 
 District of New York, 1842) ; Lewis Beck (Report on Mineralogy of New 
 York, 1842) ; T. S. Hunt (Mineral Physiography and Physiology, 443-447) ; 
 and Amer. Journ. Sci. ii. xxvi. 1858, 237 ; Geological Hist, of Serpentines 
 (Trans. Roy. Soc. Canada, i. 174) ; and J. D. Dana (Manual of Geology, 
 p. 233, third edition), as referring to it more or less in detail. 
 
KIMBEELITE FEOM THE UNITED STATES 59 
 
 compact base containing numerous lighter spots, with a 
 sharp crystal outline, thus producing a porphyritic structure. 
 Some singular blood-red patches are scattered through 
 this rock. The first type, under the microscope, appears 
 as a medium-grained aggregate of brown mica, of octahedral 
 crystals of two minerals one yellow and transparent, the 
 other black of green or colourless serpentine, and of 
 carbonates. Through this matrix occasional larger crystal 
 forms are scattered. In spite of nearly all the substance 
 of the rock being secondary, these preserve the shape of 
 crystals. Among the minerals present Professor Williams 
 identifies olivine or enstatite ; the latter being completely, 
 the former mostly, replaced by serpentine. The mica is 
 the peculiar brown biotite, well known to be characteristic 
 of eruptive peridotites, without a definite crystal form, and 
 often with a bleached peripheral zone. Of the octahedral 
 minerals, the opaque are usually chromite, but a few may 
 be magnetite, the transparent are proved to be perovskite. 
 
 The second type of this rock, under the microscope, is 
 identical with the former, except as regards structure. 
 The ground-mass is finer grained, thus throwing the 
 characteristic crystal forms of the olivine and enstatite 
 into sharp relief ; the octahedral crystals are much 
 smaller than in the other rock and are confined wholly to 
 the ground-mass ; the brown mica is less abundant. * The 
 persistence of structure in this rock, in spite of the 
 profoundest chemical changes, is remarkable. In ono 
 porphyritic specimen, the ground-mass is almost all car- 
 bonate, the mica has become quite colourless, and the olivine 
 crystals are changed to a perfectly isotropic, colourless 
 substance, enclosing the sharpest possible rhombohedra of 
 dolomite ; in fact none of the original components remain, 
 except the chromites, and yet the structure is just as sharp 
 and characteristic as in a specimen,' of which Professor 
 Williams gives a figure. 
 
 The rock, when Professor Williams wrote his earlier 
 paper, was no longer visible, being concealed beneath 
 
60 K1MBEELITE FEOM THE UNITED STATES 
 
 a lawn and a street. His description was founded upon 
 observations made and specimens collected, about 1887, 
 by Professor Oren Boot, who found it to be associated with 
 shales and limestone belonging to the Onondaga salt-group, 
 and considered it, for reasons which he gives, to be intrusive 
 in them. 
 
 In a later paper l Professor Williams adds some 
 interesting details. In cutting some deep sewers, ' two 
 admirable sections ' had been exposed. In these it was seen 
 that the serpentine formed a dyke, cutting perpendicularly 
 across the nearly horizontal strata of limestone, forcing its 
 way in places between them, and, in one of the exposures, 
 considerably disturbing those in its immediate vicinity. 
 Much of the serpentine was full of angular fragments of 
 other rocks embedded in it, sometimes at least one-third of 
 the face of a block being occupied by fragments. Most of 
 these, but by no means all, are bits of the adjacent lime- 
 stone. One, for instance, is a large fragment of black 
 shale (probably Utica shale), which here is over 1,000 feet 
 below the surface. Another is a fragment of an acid 
 crystalline rock, granite or gneiss, which must lie over 
 2,000 feet below the surface. Granitic and syenitic frag- 
 ments were also mentioned by the earliest observers. All 
 of the included limestone fragments show signs of contact 
 metamorphism, and the new minerals, thus produced, have 
 a zonal arrangement. 
 
 Professor Williams is of opinion that the eruptive 
 rock, which is now represented by the serpentine, must 
 have differed much from its present composition as repre- 
 sented in analyses furnished by Professor James Ball, 
 which he quoted in the earlier memoir. The specimen 
 consisted of carbonate of lime 34*77, carbonate of magnesia 
 2'73, and serpentine 62-5. The composition of the last 
 was as follows : 
 
 Hull. Geol Soc. Amer. i. 1890, p. 533, 
 
KIMBEELITE FROM THE UNITED STATES 61 
 
 Si0 2 . -* . . * :* 40-67 
 
 A1 2 3 . / '.; . . :* 5-13 
 
 FeO . V . . "V <. 8-12 
 
 MgO . , . . & > 32-61 
 
 H 2 . % . . * + 12-77 
 
 99-30 
 
 (2) Rock of Elliott County, Kentucky : 
 
 This rock occurs between Isom and Critche's Creeks, 
 near Fielden Post Office, six miles south-west of Willard, 
 in Elliott County, Kentucky. Mr. Diller describes it at 
 some length in the ' Bulletin of the American Geological 
 Survey,' l and, more shortly, in the American Journal of 
 Science. 2 
 
 It was discovered by Professor A. K. Crandall, who 
 states that it has a very limited extent laterally, and so 
 readily disintegrates as not to form a noticeable feature in 
 the topography. ' It appears to extend in two diverging 
 lines from Critche's Creek into the -valley of Isom's Creek, 
 with several minor offshoots of undetermined, but doubt- 
 less limited, extent, possibly no more than wedge-like 
 projections from the main dyke between the strata of the 
 coal measures, which make up the whole height of the 
 hills of this region. The whole length of the dyke in its 
 greatest surface extension appears to be less than a mile, 
 with a width of from a few feet to 50 feet or more.' 3 The 
 rock, according to Mr. Diller, is compact in structure, dark 
 greenish in colour, with a specific gravity of 2-781, having 
 embedded in it many grains of yellowish olivine, uni- 
 
 1 No. 38 (with map and illustrations). 
 
 2 Vol. xxxii. p. 121. See, also, Science, 1885, p. 65. 
 
 3 This statement is mainly an inference, as pointed out by Mr. Diller, 
 from the presence of pyrope and ilmenite in the soil. The visible outcrops 
 of the rock are only live in number three of them in a line about three fur- 
 lorigs long ; the others being about five furlongs away in opposite directions 
 from one end of it, which happens to be the spot where the rock is in best 
 preservation ; they are more or less oval in shape. 
 
62 KIMBERLITE FROM THE UNITED STATES 
 
 formly distributed throughout the mass. These, however, 
 occasionally disappear, and the whole is serpentine. 
 This olivine and the serpentine together form nearly 75 
 per cent, of the rock. Besides them other minerals 
 appear in the hand specimen, the most important being 
 pyrope and ilmenite ; a few scales of biotite may be 
 observed. Near the exposed surface the rock becomes 
 yellowish, due to the oxidation of the iron, and softer, so 
 that it readily disintegrates. 1 The garnet and much of 
 the ilmenite withstand the atmospheric influences, and are 
 found quite fresh and abundant in the sand resulting from 
 the disintegration of the peridotite. The specimens from 
 some localities are quite free from included fragments, 
 while those from another ' are full of fragments of shale, 
 which have been greatly indurated and metamorphosed in 
 the operation.' In the best preserved specimens (which 
 also are free from rock fragments) Mr. Diller estimates the 
 composition to be as follows : 
 
 Primary minerals 
 
 \ 
 
 Per cent. 
 
 Secondary minerals 
 
 Per cent. 
 
 Olivine 
 
 
 40 
 
 Serpentine . 
 
 . 30-7 
 
 Enstatite . < 
 
 
 1 
 
 Dolomite 
 
 . 14 
 
 Biotite . , 
 
 
 1 
 
 Magnetite . . 
 
 . 2 
 
 Pyrope 
 
 
 8 
 
 Octahedrite 2 . 
 
 . 1-1 
 
 Ilmenite 
 
 
 2-2 
 
 
 
 Apatite . 
 
 
 trace 
 
 
 
 He gives a figure of a microscopic section from which 
 it would appear that the larger included minerals are 
 somewhat irregular in outline, size, and distribution. The 
 olivine grains are generally irregular in form, varying from 
 Ol to 1*5 mm. in diameter, and penetrated by many 
 fissures. Occasionally, however, they occur in short 
 prism?, terminated by brachydomes, the usual planes 
 being suppressed. The structure of the matrix appears to 
 be fine-granular. The alteration of the olivine to serpen- 
 
 1 Compare the ' yellow ground ' of the mines at Kimberley. 
 
 2 A synonym of anatase (TiO.J ; and corresponding with the perovskite 
 of Williams. 
 
KIMBEELITE FROM THE UNITED STATES 63 
 
 tine takes place rapidly in the cross fractures approximately 
 parallel to the base, but very slowly along the numerous 
 minute fissures in the prism zone. Cleavage parallel to 
 the brachypinacoid is barely discernible. Magnetite is 
 excluded in the usual manner, and in some cases dolomite 
 appears as an ultimate product of alteration. The en- 
 statite has an irregular (corrosion) border. The biotite is 
 dark coloured, is strongly dichroic, and is sometimes sur- 
 rounded by a secondary border of biotite (differing in 
 optical properties) and of magnetite. The pyrope occurs 
 in spherical and ellipsoidal grains, varying from 1 to 12 mm. 
 in diameter, of a clear, deep-red colour, its specific gravity 
 being 3' 673. It is often surrounded by a border, the 
 outer band of which is commonly rendered opaque by a 
 dark powder, the inner one being a greyish or reddish- 
 brown colour, generally fibrous in structure (the substance 
 named kelyphite by Schrauf, but shown by Lasaulx to 
 be a mixture of several minerals, chiefly of the pyroxene 
 and amphibole groups). Of the other minerals, the 
 octahedrite occurs in yellowish clouded grains, ranging 
 in size from '004 to '06 mm. in diameter. The dolomite is 
 irregularly distributed. Of the serpentine there are two 
 forms. 
 
 This peridotite cannot be seen in contact with the 
 adjacent sandstone and shale ; but within a short distance 
 from it both appear to be indurated, and the latter in some 
 cases to be converted into a kind of spilosite. The frag- 
 ments of shale included in the peridotite are always 
 surrounded by a border of colourless mica, its scales being 
 intricately intermingled, and have undergone other mineral 
 changes, generally on a minute scale. On a review of the 
 whole evidence, Mr. Diller concludes that ' the peridotite 
 is a truly eruptive rock, which has been forced up through 
 the carboniferous strata.' 
 
 At the end of the paper Mr. Diller gives a series of 
 analyses of the adjacent sedimentary rocks, of the peridotite, 
 and of the minerals contained in it. 
 
64 KIMBEELITE FROM THE UNITED STATES 
 
 The following represent the peridotite : 
 
 i. IT. 
 
 Si0 2 ... .* 29-81 29-43 
 
 Ti0 2 .. [ft* . 2-20 1-48 
 
 PA / .' .' 0-35 trace 
 
 Cr 2 6 3 . .- . * 0-43 0-14 
 
 A1A v..:- V* .,.-' 2-01 2-36 
 
 Fe 2 3 -* : 5-16 
 
 FeO . . . , 4-35 9-06 
 
 MnO ^ * , 0-23 
 
 NiO . . . 0-05 0-60 
 
 CaO .. . ^ 7-69 694 
 
 MgO . v 32-41 31-66 
 
 K 2 . . , ; v; 0-20 0-65 
 
 Na 2 . . .. 0-11 0-78 
 
 H 2 (at 110) .. .. 8-92 10-9O 
 
 C0 2 . ^: . 6-66 5-65 
 
 SO, 0-28 0-30 
 
 Total . . * 100-86 100-15 1 
 
 S.G. . . . 2-781 2-697 
 
 To these notes may be added a few remarks on the 
 specimens which I find in Professor Lewis' collection : 
 
 The hand specimen [436] labelled * From James Street, 
 Syracuse, N. Y. (G. H. W. col. Feb. 1888)' is a dark- 
 coloured rock of a greenish tint, slightly mottled in one or 
 two places with a yellower green hue, compact in structure, 
 dull, but with fairly numerous rather rounded spots, up to 
 about one-sixth of an inch in diameter, with a more 
 glistening lustre. The specimen is traversed by a thin 
 whitish vein. In fracture and general aspect it resembles 
 a serpentine, or something between a serpentine and a 
 diabase, except for the slight irregularity in the * por- 
 
 1 Including 0'20 of sulphides. 
 
KIMBEELITE FROM THE UNITED STATES 65 
 
 phyritic ' structure. A slice has been prepared for micro- 
 scopic examination ; but here, as in the case of the others 
 mentioned below, a brief notice will suffice, after Professor 
 Lewis' elaborate description of the Kimberley rock, for 
 the general resemblance is very strong. In this slice we find 
 a number of grains, rather variable in size and form, some 
 approaching idiomorphic, others rounded or apparently 
 broken, but all serpentinised. Most of them were formerly 
 olivine, but it is possible that enstatite also may have been 
 present. There are various differences of detail in the 
 colour and minuter structure of the serpentine, in the dis- 
 tribution and arrangement of the iron oxide, and the like ; 
 but on them it is needless to dwell. These larger grains 
 are scattered about in a more or less granular matrix, 
 apparently identical with that of the Kimberley rock, in 
 which serpentine and a carbonate, probably calcite with 
 some dolomite, are important constituents. One part of 
 the slice suggests the presence of fragments of a peridotic 
 rock, embedded in a matrix of similar condition ; but 
 whether this is significant of a pyroclastic structure or of a 
 fluxion breccia is open to question. Here, also, is a small 
 ' patch ' of rather rounded mineral fragments, which seem 
 to be a felspar. 
 
 The rock from Kentucky is represented by the following 
 specimens : 
 
 (a) [435, 1.] < Dyke I., Elliott Co. (Crandall).' A rock 
 resembling that from Syracuse in colour and aspect, but the 
 fracture is a shade rougher, the rounded spots run to a 
 slightly larger size, being not seldom about one-fifth of an 
 inch in diameter ; they are less lustrous than in the other 
 case, and of a yellowish-green colour (similar to that in the 
 mottling of the other specimen and resembling that of 
 olivine), and thus lighter than the matrix. Except in this 
 respect the two specimens are very similar. Microscopic 
 examination shows that this rock closely resembles one of 
 the best-preserved specimens from Kimberley. The olivine 
 
 F 
 
66 KIMBEELITE FROM THE UNITED STATES 
 
 generally is more rounded than in the last case, and a con- 
 siderable amount of the original mineral still remains, 
 especially in the larger grains ; that is, they are about half 
 oli vine, half serpentine, exhibiting the usual structure. There 
 is one grain which appears to be a monoclinic pyroxene, con- 
 taining two or three flakelets of a micaceous mineral ; also, 
 a small grain of the usual brownish mica, a garnet with the 
 outer zone of rich brown kelyphite, already described, with 
 two others which possibly may be the same mineral more 
 completely altered and two or three smaller deep-brown 
 grains resembling chromite. One or two irregular patches, 
 consisting of a carbonate and some small minerals (zeolites) 
 are very like the irregular cavities in some scoriaceous 
 rocks, when these become converted into amygdules. I 
 suspect the presence of a small rock fragment consisting of 
 little roundish grains of olivine (or possibly malacolite) in 
 a minutely granular matrix, of which I can hardly venture 
 to say more than ' probably basic igneous.' 
 
 (b) [435, 2.] The label with this specimen (a printed 
 one on thick paper) is partly effaced by Drubbing ; it has the 
 words ' Kentucky Geological Survey . . . and Bureau of 
 (? emigration). Frankfort, Kentucky, U.S.A.' (the effaced 
 part being apparently a date, perhaps 1886). It is not dis- 
 tinctly stated to be from the above locality, but I think 
 there can be no doubt on that point. It is practically 
 identical with the last-named, except that the yellowish- 
 green spots run a shade larger, occasionally almost 
 one-quarter of an inch. Under the microscope the rock 
 appears very similar to the last described, but the olivine 
 is rather more serpentinised ; garnet as before ; one or two 
 patches of calcite with a tuft or two of an acicular zeolite, 
 suggestive of cavities of some kind ; part of the matrix 
 is tinged with green, this apparently being due to the 
 presence of minute scales of a chloritic mineral. 
 
 (c) [437.] This specimen bears the label, 'Elliott Co., Ky. 
 (Diller).' The matrix is slightly more compact than in 
 the case of the last two the yellowish spots are not quite 
 
KIMBE ELITE FROM THE UNITED STATES G7 
 
 so frequent, or so large generally, though one, which shows 
 a moderately good cleavage and is apparently olivine, attains 
 to quite a quarter of an inch. It has a distinctly rounded 
 outline. Mica also is more plentiful in this specimen, 
 occurring generally in small rounded flakes ; but these in one 
 or two cases are about one-fifth of an inch in diameter. It is 
 distinctly brown in colour. In microscopic structure the 
 rock is like the last, but without any garnet or spots 
 suggestive of filled-up cavities ; there are also one or 
 two semi-opaque grains, minutely granular in structure, 
 which are possibly fragments of some rather compact and 
 decomposed rock. 1 
 
 The above hand specimens from both Syracuse and 
 Elliott Co. are perhaps a little more like a porphyritic 
 igneous rock than those which I have seen from Kimberley, 
 owing to the absence of distinct rock fragments and the 
 more uniform size of the included minerals ; and the same 
 may be said of their microscopic structure. They are very 
 like serpentine, but the points to which attention has been 
 called produce a difference marked, though not easily ex- 
 pressed in words from the normal specimens of that rock. 
 This also is very perceptible in looking at the thin slices 
 with the unaided eye or with a common pocket lens, when 
 they are held up to the light. The rather rounded outline 
 of the enclosures, their unequal size and distribution, give 
 them a fragmental, rather than a normal porphyritic, 
 aspect. I believe that had I been asked to guess what the 
 rocks were, from the evidence of the hand specimens and 
 from this mode only of studying the slices (i.e. without 
 actually using a microscope), I should have answered 
 * probably a non-scoriaceous unstratified tuff.' 
 
 1 See Plate II. for a figure of a portion -of this specimen. 
 
NOTE 
 
 THE portions of Professor Lewis' manuscripts which, as 
 explained in the Preface, ha.ye not been printed, brought 
 out more clearly one point in regard to the origin of the 
 diamond than is done in the two papers included in this 
 work, though I remember he laid stress on it in giving a 
 summary of the second paper at Manchester. This was 
 the intimate connection of peridotite (or serpentine) with 
 the diamond, which he regarded as being in the relation of 
 cause and effect, at least in South Africa and in Kentucky, 
 where carbonadoes occur under similar conditions. This 
 will appear from the report of his paper printed in the 
 Geological Magazine' (1888, pp. 129-131). It may 
 suffice to quote the concluding sentence : ' All the facts thus 
 far collected indicate serpentine in the form of a decom- 
 posed eruptive peridotite as the original matrix of the 
 diamond.' Professor Lewis, I believe, thought that, owing 
 to the basic nature of the peridotite, the carbon in the 
 sedimentary rock with which it came into contact was 
 less likely to be oxidised than it would be by more acid 
 intrusives, but this opinion, so far as I know, is not ex- 
 pressed in his published papers. 
 
 I may add that in 1896 the workings in the De Beers 
 Mine had reached a depth, of over 1,500 feet. They have 
 ceased to work the diamond-bearing rock by excavating it 
 vertically downwards from the top of the ' pipe,' but sink 
 shafts through the * country rock ' (shale, quartzite, and 
 ' melaphyre '), from which they drive levels into the pipe 
 itself, removing its contents by means of these, as it were, 
 
NOTE 69 
 
 layer by layer. While the last sheets of this book were in the 
 press Sir J. B. Stone, M.P., F.G.S., sent me a collection of 
 specimens which he had recently received from this mine, 
 among which were pieces of the diamond-bearing rock, of 
 which the deepest was labelled 1,400 feet, and I saw blocks 
 from nearly as far down in a collection shown to me by 
 Mr. W. Crookes, F.R.S. A particularly well-preserved 
 specimen which he has lent to me for study came from 
 1,320 feet. 
 
 He has also favoured me with a copy of a section re- 
 presenting the workings in this De Beers mine. The shaft 
 has reached a depth of quite 1,500 feet, and from it the 
 lowest level is being driven. The section of the ' country 
 rock,' outside the ' pipe ' containing the diamond- bearing 
 breccia, is as follows : (1) superficial debris, (2) basalt, (3) 
 black shale, (4) 'melaphyre,' (5) quartzite, (6) 'slate' pro- 
 bably only a hard shale, (7) quartzite and ' slate.' Dykes 
 (probably basaltic) pierce into (5), through (6) and (7). 
 The ' melaphyre ' (4) is about four hundred feet thick. The 
 area of the workings is twenty-two acres. It is the least 
 of the four mines mentioned on page 1 ; Du Toits Pan, 
 the largest, being forty-five acres. Since Professor Lewis 
 wrote, another important mine (the Wesselton) has been 
 opened ; it is included within the same circle as the last- 
 named. 
 
 T. G. B. 
 
INDEX 
 
 AERINITE, 15 
 
 Africa (South), first diamond found 
 
 in 1870, 1 
 
 Age of diamond-bearing ' pipes,' 7 
 Agglomeratic matrix, 53 
 Analyses, diamond-bearing rock, 5, 
 
 47 
 Analysis, bronzite, 20 
 
 Kimberlite, 61 
 
 Mica, 28 
 
 Peridotite, 64 
 
 Serpentine, 61 
 
 Smaragdite, 19 
 
 Vaalite, 28 
 Anatase, 62 
 Apatite, 37 
 
 ' Augengneiss,' 53 
 
 BALL, J., 60 
 
 Bastite, 19 
 
 Baumhauer, E. H. von, 32 
 
 Beck, L., 58 
 
 Becke, F., 24 
 
 ' Blue ground,' 3 
 
 the diamond matrix, 44 
 Bonney, T. G., 55, 68 
 
 on Kimberlite, 58 
 Boricky, E., 34 
 Bourgeois, 35 
 Breithaupt, A., 36 
 Brewster, D., 44 
 
 ' Brockengesteine,' 54 
 Brogger, W. C., 53 
 Bronzite, 4, 19 
 
 analysis, 20 
 Bulfontein Mines, 1 
 Butler, P. J., 44 
 
 CALCITE, 38 
 ' Calc-tuff,' 38 
 Cataclastic structure, 53 
 
 ! Chalcedony, 39 
 
 diaper, M., 55 
 j Chassignite, 56 
 
 Chondrites, 56 
 
 Chrome-diopside, 21 
 
 Chromite, 36 
 
 Cohen, E., 3, 7, 38, 52 
 
 Colesberg Kopje, shale in volcanic 
 pipes, 4 
 
 Colonial Exhibition, 3, 8 
 
 Connecticut, smoky quartz, 43 
 
 Cooper, G. C., 44 
 
 ' Country rock,' 3, 8, 68 
 
 Crandall, A. K. , 35, 61 
 
 Crookes, W., 69 
 
 Cross, C. W., 26 
 
 Cyanite, 39 
 
 DANA, J. D., 58 
 Dathe, E., 26 
 Davies, T., 4 
 De Beers Mines, 1, 8, 68 
 
 1885, section, 8, 69 
 1 Demantoid,' 28 
 Descloiseaux, A., 32, 44 
 Diallage, 4 
 Diamond, 40 
 
 history of, 1 
 
 Diamond-bearing peridotite, 1 
 ' pipes,' age of, 7 
 
 matrix, 44 
 
 Diamonds, liquid carbonic acid in, 
 43 
 
 minute, 41 
 
 Russian, 29 
 Diller, J. S., 35, 61 
 Doelter, C., 22, 48 
 Doll, E., 44 
 
 ' Dry diggings,' 2 
 Du Toits Pan Mines, 1, 20 
 1885, section, 3 
 Dumas, J. B., 44 
 
INDEX 
 
 71 
 
 Dumour, A. A., 44 
 
 Dunite, 49 
 
 Dunn, E. J., 3, 6, 52 
 
 ELLIOTT Co. (Ky.), Kimberlite, 56, 58, 
 
 61, 65, 66 
 
 Enclosures, fragmentary, 45 
 ' Eozoonal ' structure, 18 
 Epidote, 37 
 
 Estherville meteorite, 54 
 Euganean Hills (Italy) breccia, 55 
 Euphoticle, 4 
 4 Eye-gneiss,' 53 
 
 FIZEAU, A. H. L., 43 
 Flight, W., 5, 20, 27, 52 
 Fouque, F., 41 
 
 GABBRO, decomposed, 4 
 Garnet, 28 
 Gibbsite, 45 
 Griesbach, C. L., 7 
 Griqua Land mines, 2 
 Groth, P., 32 
 Ground-mass, 45 
 chemical composition, 46 
 
 HAIDINGER, W. von, 57 
 Harting, P., 43 
 Hawes, G. W., 43 
 Hedley, T., 7, 42 
 Herwig, F., 22 
 Hudleston, W. II., 7, 52 
 Hunt, T. S., 58 
 Hussak, E., 18, 34 
 
 IGNEOUS lava,' matrix a true, 52 
 Ilmenite, 37 
 Inclusions, diamond, 43 
 
 JANNKTTAZ, E., 43 
 Jeremejew, P. von, 40 
 Jones, T. K., 4, 7, 9 
 Judd, J. W., 27 
 
 KALKOUSKY, E., 26 
 Karoo beds, 7 
 (Upper) plateau, 2 
 Kenngott, G. A., 43 
 
 Kentucky, Kimberlite, 56, 61, 65, 66 
 
 peridotite, 35 
 Kimberley (S. Africa) Mines, 1 
 
 diamonds, 43 
 Kimberlite, 50 
 
 analysis, 61 
 
 composition of, 62 
 
 Kentucky, 56, 61 
 
 New York State, 56, 58 
 Kjerulf, T., 49, 53 
 Klein, J. F. C., 32 
 Knop, A., 37, 41 
 Koksharow, N. von, 32 
 Kunz, G. F., 40 
 
 LAVA, porphyritic, 51 
 
 Lemberg, J., 49 
 
 Levy, A. Michel- ; see Michel-Levy, A. 
 
 Lewis, H. Carvill, on ' Matrix of the 
 
 Diamond,' 10, 68 
 collection of rocks, 58, 64 
 Limburgite, 55 
 Losch, A., 29 
 
 MAGNETITE, 36 
 
 Maskelyne, N. S., 5, 20, 27, 52 
 
 Matrix, diamond, 10, 44 
 
 minerals, 11 
 Melilite, 49 
 Meteorites, 54, 57 
 Mica, 25 
 
 analysis, 28 
 Michel-Levy, A., 23, 41 
 ' Mimetic minerals,' 32 
 Minerals, diamond, 11 
 
 matrix, 44 
 
 ' Mortel-structur,' 53 
 Moulle, A., 40, 52 
 
 NAUMANN, C. F., 54 
 'Nephelin-pikrit,' 34 
 New York State, Kimberlite, 56, 58 
 peridotite, 35 
 
 OCTAHEDRITE, 62 
 
 Olivine, 9, 12, 17 
 
 surrounded by perovskite, 34 
 ' Olivinfels,' 49 
 Ophicalcite, 48 
 
 Orange Free State Mines, 2 
 
 River diggings, 1 
 Orthite, 37 
 
72 
 
 INDEX 
 
 PERIDOTITE, 17, 42, 68 
 
 analyses, 64 
 
 Perovskite, 29, 31, 32, 33, 34, 36 
 
 Petzhold, A., 44 
 
 Picotite, 36 
 
 Picrite-porphyrite, 50 
 
 4 Pipes,' volcanic, 4 
 
 Pleistocene depression, 38 
 
 Porphyritic lava, 51 
 
 Pyroxenic minerals, 19 
 
 QUARTZ, liquid carbonic acid in, 43 
 
 EAMMELSBERG, C. F., 28, 48 
 
 Eath, (jr. Vom, see Vom Bath 
 
 Eeunert, T., 40 
 
 Eeusch, H. H., 53 
 
 Eeyer, E., 55 
 
 Eoot, O., 60 
 
 Eoscoe, Sir H. E., 51 
 
 Eosenbusch, H., 9, 18, 23, 26, 49, 58 
 
 Eoth, J., 54 
 
 Eussian diamonds, 29 
 
 Eutile, 16 
 
 SANDSTONE in volcanic ' pipes,' 4 
 
 Saude, Ben, 32 
 
 Sauer, A., 33, 34 
 
 Schrauf, A., 23 
 
 Serpentine, 7, 12, 21, 38, 68 
 
 analysis, 61 
 
 Shale fragments surrounded by cal- 
 
 cite, 46 
 
 Shale in volcanic ' pipes,' 4 
 Shaw, J., 3, 9 
 Sjogren, 37 
 
 Smaragdite, analysis, 19 
 Sorby, H. C., 44 
 Sphene, 38 
 
 Stelzner, A., 34, 48, 49 
 Stone, Sir J. B., 45, 69 
 
 Stow, G. W., 3, 7 
 
 Syracuse (N.Y.), Kimberlite, 56, 58 
 
 Syssersk (Urals), 29 
 
 TALC, 38 
 
 Titanic iron in perovskite, 33 
 
 Titaniferous magnetite, 36 
 
 Tornebohm, A. E., 23, 37, 49 
 
 Tourmaline, 38 
 
 ' Trapp-eisenerz,' 36 
 
 Tremolite, 14, 38 
 
 Triassic (post-) age of diamond, 7, 10 
 
 Tschermak, G., 20, 22, 32, 49, 50, 57 
 
 UNITED STATES, Kimberlite, 56, 58 
 Urot Mines, 2 
 
 VAAL Eiver diggings, 1 
 
 dykes, 9 
 Vaalite, 5, 28 
 
 analysis, 28 
 Vanuxem, L., 58 
 
 Volcanic intrusions in Karoo beds, 7 
 Volcanic ' pipes,' 4 
 Vom Bath, G., 22, 37 
 
 WADSWORTH, M. E., 23, 53, 54 
 
 Wales, volcanic breccia in, 55 
 
 Wiik, F. J., 22 
 
 Williams, G. H., 26, 35, 58, 60 
 
 Wohler, F., 44 
 
 Wright, A. W., 43 
 
 YELLOW ground,' 3, 62 
 
 ZEOLITES, 39 
 
 Zirkel, F., 13, 26, 27, 33, 43 
 
 PRINTED BY 
 
 SPOTTISWOODE AND CO., NEW-STREET SQUARE 
 LONDON 
 
PLATE II. Microscopic Sections of Kimberlite. 
 
 (i) THE KIMBERLEY ROCK. 
 
 (2) THE NORTH AMERICAN ROCK. 
 

 ->--ff '" - 
 
April, 1896. 
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 Physiology. By W. B. McNAB, M.D. 
 With 42 Diagrams. Is. Qd. 
 
 Thermodynamics. By BICHARD WOB- 
 MELL, M. A., D.Sc, With 41 Diagrams. 
 Is. Qd. 
 
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