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Title: Diamonds
Author: Crookes, William
Language: English
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HARPER’S LIBRARY _of_ LIVING THOUGHT
[Illustration: (publisher colophon)]
[Illustration:
DIAMONDS
BY
SIR WILLIAM
CROOKES
HARPER &
BROTHERS
LONDON & NEW YORK]
[Illustration: THE CULLINAN DIAMOND.
From a photograph by the Author. (See pages 76-79.)
Frontispiece.]
·DIAMONDS·
BY
SIR WILLIAM CROOKES
LL.D., D.Sc., F.R.S.
Foreign Sec. R.S., Hon. LL.D. (Birmingham), Hon. Sc.D. (Camb.
and Dubl.), Hon. D.Sc. (Oxon. and Cape of Good Hope); Past Pres.
Chem. Soc., Brit. Assoc., Inst. Elect. Eng., Soc. Psych. Res.;
Hon. Mem. Roy. Phil. Soc. Glasgow, Roy. Soc. N.S.W., Pharm. Soc.,
Chem. Metall. and Mining Soc. of South Africa, Amer. Chem. Soc.,
Amer. Philos. Soc., Roy. Soc. Sci. Upsala, Deutsch. Chem. Gesell.
Berlin, Psychol. Soc. Paris, “Antonio Alzate” Sci. Soc. Mexico.
Sci. Soc. Bucharest, Reg. Accad. Zelanti, Aci Reale; Corresp.
Inst. de France (Acad. Sci.), Corresp. Mem. Bataafsch Genoots.
Rotterdam, Soc. d’Encouragement pour l’Indust. Paris, For. Mem.
Accad. Lincei Rome.
WITH 24 ILLUSTRATIONS
LONDON AND NEW YORK
HARPER & BROTHERS
45 ALBEMARLE STREET, W.
1909
TO MY WIFE
MY COMPANION AND FRIEND OF
FIFTY-FOUR YEARS.
TO HER JUDGMENT AND ADVICE I OWE MORE
THAN I CAN EVER REPAY
AND TO HER I DEDICATE THIS BOOK.
PREFACE
The following pages are based on personal observations during two
visits to Kimberley, in 1896 and 1905, and on personal researches
on the formation and artificial production of diamonds. In 1896 I
spent nearly a month at Kimberley, when Mr. Gardner F. Williams,
the General Manager of the De Beers Consolidated Mines, and the
managers of neighbouring mines, did their utmost to aid in my
zealous quest for reliable information. They gave me free access
to all workings above and below ground, allowed me to examine at
leisure their stock and to take extracts from their books. I had
exceptional opportunities of studying the geology of the Diamond
and of noting the strange cataclysmal facts connected with the
birth, growth, and physics of the lustrous stones.
In 1905 with my wife I returned to Kimberley. We were members of
the British Association which held its meeting that year in South
Africa. I was asked to give one of the Association lectures at
Kimberley and it was natural for me to discourse “On Diamonds.”
During our stay we were the guests of Mr. Gardner Williams.
Returning to England after the visit of 1896, I gave two
lectures on Diamonds at the Imperial Institute and one at the
Royal Institution. These lectures, and the lecture delivered at
Kimberley, in 1905--hitherto only privately distributed--form
the basis of the present volume. On each visit I took abundant
photographs, many of which I now reproduce. A few are copied
from plans lent by Mr. Gardner Williams and one or two are from
photographs purchased at Kimberley.
In obtaining statistical information of the Diamond industry, I owe
much to the Annual Reports of the De Beers Company. I have also
quoted freely from Reunart’s valuable book on _Diamonds and Gold in
South Africa_; and I render my acknowledgments to the authors of
the following papers and memoirs.
_On a Visit to the Diamond Fields of South Africa, with Notices of
Geological Phenomena by the Wayside._ By John Paterson, Esq., M.A.
_On the Mode of Occurrence of Diamonds in South Africa._ By E. J.
Dunn.
_On the Origin and Present Position of the Diamonds of South
Africa._ By G. G. Cooper, Esq., of Graaf Reinet.
_On the Character of the Diamantiferous Rock of South Africa._
By Prof. N. Storey Maskelyne, F.R.S., Keeper, and Dr. W. Flight,
Assistant in the Mineral Department, British Museum.
_Further Notes on the Diamond Fields of South Africa._ By E. J.
Dunn.
_Notes on the Diamond Fields of South Africa, 1880._ By E. J. Dunn.
_Analogies between the Diamond Deposits in South Africa and those
in Meteorites._ By M. Daubrée.
_Notes on the Diamond-bearing Rock of Kimberley, South Africa._ By
Sir J. B. Stone, Prof. T. G. Bonney, and Miss Raisin.
_Notes on the Diamond Rock of South Africa._ By W. H. Hudleston.
_The Parent Rock of the Diamond in South Africa._ By the Reverend
Professor T. G. Bonney.
The Presidential Address, by Grove Carl Gilbert, to the Geological
Society of Washington, on _The Origin of Hypotheses. Illustrated by
the Discussion of a Topographical Problem._ 1896.
_Le Four Electrique._ By Henri Moissan. 1897.
_The Diamond Mines of South Africa._ By Mr. Gardner F. Williams.
(In this publication the story of the rise and development of the
industry is exhaustively narrated.)
_British Association, South African Meeting, 1896, Kimberley
Handbook._
_The Meteor Crater of Canyon Diablo, Arizona; its History, Origin,
and Associated Meteoric Irons._ By George P. Merrill. 1908.
In the present volume I have tried to give some idea of the
underground wonders of the Kimberley mines. I have pictured the
strenuous toil of the men who bring to the surface the buried
treasures, and I have given some idea of the skill and ingenuity
with which their labours are controlled. I have done my best to
explain the fiery origin of the Diamond, and to describe the
glowing, molten, subterranean furnaces where they first begin
mysteriously to take shape. I have shown that a diamond is the
outcome of a series of Titanic earth convulsions, and that these
precious gems undergo cycles of fiery, strange, and potent
vicissitudes before they can blaze on a ring or a tiara.
I am glad to have paid these two visits to South Africa. I always
recall with interest the dusky smiling natives at work and at
play. I am glad to have seen that Arabian Nights vision, the
strong-room of the De Beers Company. Above all, I have vividly
graven on my heart the friendly welcome, and the innumerable acts
of kindness shown us by our able, energetic, and enterprising
Colonial fellow-countrymen.
W. C.
CONTENTS
CHAPTER PAGE
I. PRELIMINARY 1
II. KIMBERLEY AND ITS DIAMOND MINES 14
III. KIMBERLEY MINES AT THE PRESENT DAY 34
IV. COLLECTING THE GEMS 55
V. THE DIAMOND OFFICE 73
VI. NOTEWORTHY DIAMONDS 76
VII. BOART, CARBONADO, AND GRAPHITE 81
VIII. PHYSICAL AND CHEMICAL PROPERTIES OF
THE DIAMOND 89
IX. GENESIS OF THE DIAMOND 115
X. THE NATURAL FORMATION OF THE DIAMOND 127
XI. METEORIC DIAMONDS 134
INDEX 141
LIST OF PLATES
The Cullinan Diamond, from a photograph by the
Author (see pp. 76-79) _Frontispiece_
FIG. FACING PAGE
1. River Washings at Klipdam 10
2. Plan of the Kimberley Diamond Mines 10
3. Kimberley Mine. The “Pipe” 18
4. Section of Kimberley Mine 18
5. Wesselton Diamond Mine. Open Workings 34
6. De Beers Compound 40
7. De Beers Mine. Underground Workings 40
8. De Beers Washing and Concentrating Machinery 48
9. Sorting Concentrates for Diamonds. De Beers 54
10. De Beers Diamond Office. 25,000 carats 72
11. De Beers Diamond Office. The Valuators’ Table 72
12. A group of large Diamond Crystals 76
13. Some Historic Diamonds 80
14. Crystalline forms of native Diamonds 86
15. Triangular Markings on natural face of a Diamond
Crystal 88
16. Triangular Markings artificially produced on a
Diamond Crystal 88
17. Diamond-cut Glass and Shavings 98
18. Diamonds in Röntgen Rays. A. Black Diamond
in gold frame. B. Pink Delhi Diamond.
C. Paste Imitation of B. 98
19. Curve of Vapour Pressure of Carbon _page_ 113
20. Moissan’s Electric Furnace 116
21. Artificial Diamond made by the Author from
molten iron 120
22. Moissan’s Artificial Diamonds 120
23. Diamonds from Canyon Diablo Meteorite 138
DIAMONDS
CHAPTER I
PRELIMINARY
From the earliest times the diamond has fascinated mankind. It
has been a perennial puzzle--one of the “riddles of the painful
earth.” It is recorded in _Sprat’s History of the Royal Society_
(1667) that among the questions sent by order of the Society to
Sir Philiberto Vernatti, Resident in Batavia, was one inquiring
“Whether Diamonds grow again after three or four years in the same
places where they have been digged out?” The answer sent back was,
“Never, or at least as the memory of man can attain to.”
In a lecture “On Diamonds,” fifty years ago,[1] Professor Maskelyne
said, “The diamond is a substance which transcends all others in
certain properties to which it is indebted for its usefulness in
the arts and its beauty as an ornament. Thus, on the one hand, it
is the hardest substance found in nature or fashioned by art. Its
reflecting power and refractive energy, on the other hand, exceed
those of all other colourless bodies, while it yields to none in
the perfection of its pellucidity.” He was constrained to add, “The
formation of the diamond is an unsolved problem.”
Diamonds are found in widely separated parts of the globe. In the
United States they have been found in Arkansas, where the work of
testing the deposits is now going on steadily and quietly. The
general geology and petrography of the area and the weathering of
the peridotite are described in a paper read before the American
Institute of Mining Engineers by Messrs. Kunz and Washington. In
tests made with a diamond drill the peridotite was proved to
depths of 200 feet. The green and yellow grounds underlying the
layer of black, sticky soil are found to extend down 40 feet in
places, and are estimated to average 20 feet in depth over the
area. The outcrop of the peridotite is estimated to cover about
40 acres, and may be larger. Some 540 diamonds have been found,
with an aggregate of 200 carats. The largest stone weighs about
6·5 carats, though the average size compares favourably with the
general run of most of the South African mines. There is a large
proportion of white stones, many of which are free from flaws and
are very brilliant. The genuineness of the occurrence of diamonds
in their matrix is again proved, one stone having been found
imbedded in the green ground at a depth of 15 feet. This peridotite
has the form of a volcanic pipe, and therefore its outcrop is
limited to one place.
In California authentic finds of diamonds are recorded in Butte
County, especially at Cherokee, above Orville. These diamonds,
however, have come from alluvial deposits and have been found
generally in washing for gold. As yet no authenticated discovery of
diamond in its original matrix in California is recorded.
In Brazil the diamond industry has been increasing of late years,
and the old mines in the Diamantina country are being worked by
American capital and by the American methods which have proved so
successful at De Beers. It is estimated that the annual value of
the diamonds exported from Brazil amounts to over £800,000, but
it is impossible to arrive at accurate figures owing to the large
quantities smuggled out of the country to avoid payment of the
export tax.
British Guiana produces a small quantity of diamonds, mostly,
however, of small size. Between January and September, 1907, 1564
carats were exported.
Indian diamonds chiefly come from the states of Panna, Charkhari,
and Ajaigarh. In 1905 India exported 3059 carats, valued at £5160.
CAPE COLONY
It is a standing surprise to the watchful outsider how little
attention is bestowed on some of our colonies. For instance, to
the Cape Colony, comprising vast, varied, and productive regions,
we have till recently manifested profound ignorance and consequent
indifference. When the Cape Colony was first incorporated with
the Empire, it was pronounced “a bauble, unworthy of thanks.” Yet
before the Suez Canal and the Waghorn overland route to India, the
Cape, as commanding our road to India, Australia, and China, had a
special importance. Even now it presents an alternative route which
under conceivable circumstances may be of capital moment.
The high grounds above Cape Town are rich in medicinal
health-giving waters. The districts where these springs occur
are high-lying, free from malaria, and admirably adapted for the
restoration of invalids. It needs only some distinguished power to
set the fashion, some emperor, prince, or reigning beauty to take
the baths and drink the waters, and the tide of tourists would
carry prosperity to Aliwal North, Fraserburg, Cradock, and Fort
Beaufort.
South Africa, as I shall endeavour to show in detail, is the most
important source of diamonds on the earth, and ranks with Australia
and California as one of the three great gold-yielding regions. But
the wealth of South Africa is not only in its gold and diamonds.
The province of Natal contains more coal than Britain ever owned
before a single bucket had been raised, and the beds extend over
the Orange River Colony, whilst valuable iron ores exist also in
large quantities.
In the year 1896 I spent nearly a month at Kimberley. Mr. Gardner
F. Williams, General Manager of the De Beers Consolidated Mines,
and the Managers of neighbouring mines, did their utmost to assist
me in my inquiries and to ply me with valuable information. I had
full access to all the workings, above and below ground, and was
able to examine at leisure their stock and take extracts from their
books.
Again, in the year 1905, I paid another visit to Kimberley as the
guest of Mr. Gardner Williams on the occasion of the meeting of the
British Association in South Africa.
RIVER WASHINGS
Besides the matrix mines, where the stones are found in pipes
supposed to be of volcanic origin, the alluvial deposits on the
Vaal River are of considerable importance. The terraces and gravels
along the Vaal River for about 200 miles have been worked for
diamonds, the deposits sometimes extending several miles on each
side of the river, and varying from a few inches to 40 or 50 feet
in thickness. The diamonds are found almost everywhere through the
gravel deposit.
Before describing the present mode of diamond extraction followed
in the important mines, I will commence with these “River
Washings,” where, in their primitive simplicity, can be seen the
modes of work and the simple machinery long since discarded in
the large centres of the industry. The drift or so-called “river
washings” present a very interesting phase of diamond industry. The
work is carried on in the primitive fashion adopted in the early
days of diamond discovery, every man working on his own little
claim, assisted by a few natives, and employing primitive machinery
(Fig. 1). The chief centre of the Vaal River washings is about 30
miles to the north-west of Kimberley, at a place called Klipdam
No. 2. There was originally a Klipdam a few miles further, and
here the miners congregated, but the exhaustion of their claims
made them migrate to others not far off and reported to be richer.
Here, accordingly, they re-erected their iron houses and called it
Klipdam No. 2.
It is a mistake to speak of “river washings.” The diamantiferous
deposits are not special to the old or recent river bed, but appear
to be alluvial deposits spread over a large tract of country by
the agency of water, which at some period of time subsequent to
the filling up of the volcanic pipes planed off projecting kopjes
from the surface of the country and scattered the debris broadcast
over the land to the north-west of Kimberley. The larger diamonds
and other heavy minerals would naturally seek the lowest places,
corresponding with the river bed, past and present. The fact that
no diamonds are found in the alluvial deposits near Kimberley
may perhaps be explained by supposing that the first rush was
sufficiently strong to carry the debris past without deposition,
and that deposition occurred when the stream slackened speed. At
Klipdam No. 2 the diamantiferous earth is remarkably like river
gravel, of a strong red colour--quite different from the Kimberley
blue ground--and forms a layer from 1 to 8 feet thick, lying over
a “hard pan” of amygdaloidal trap, the melaphyre of the Kimberley
mines.
[Illustration: FIG. 1. RIVER WASHINGS AT KLIPDAM.]
[Illustration: FIG. 2. PLAN OF THE KIMBERLEY DIAMOND MINES.
To face p. 10.]
When I was at Klipdam the miners had congregated at a spot
called “New Rush,” where some good finds of diamonds had been
reported. The gravel is dug and put into a machine resembling
the gold miner’s dolly, where it is rocked and stirred by rakes,
with a current of water flowing over it. Here all the fine stuff
is washed away and a rough kind of concentration effected. The
residual gravel is put on a table and sorted for diamonds--an
operation performed by the master. At one of the claims where
work was proceeding vigorously I asked the proprietor to let
me be present at the sorting out, as I should like to see river
diamonds. He willingly consented, but no diamonds were to be found.
On my expressing regret, he said he had not seen a diamond for a
fortnight! I remarked that the prospect was rather a poor one,
but he told me that a fortnight before he picked out one worth
£300, “and that,” he said, “will pay for several weeks’ wages of
my boys.” This is the kind of speculative gambling that goes on at
the river diggings. The miner may toil fruitlessly for months, and
then come across a pocket of stones, where they have been swept by
some eddy, by which he will net several thousands. Diamonds from
the “river washings” are of all kinds, as if contributed by every
mine in the neighbourhood. They are much rolled and etched, and
contain a good proportion of first-class stones; they are of very
good quality, as if only the better and larger stones had survived
the ordeal of knocking about. Diamonds from the drift fetch about
40 per cent more than those from Kimberley; taking the yield of the
Kimberley and De Beers mines as worth all round, large and small,
26s. 6d. a carat, those from the drift are worth 40s.
As a rule the better class of natives--the Zulus, Matabeles,
Basutos, and Bechuanas--when well treated, are very honest and
loyal to their masters. An amusing instance of the devotion of a
Zulu came to my knowledge at Klipdam. He had been superintending
a gang of natives on a small claim at the river washings. It
yielded but few stones, and the owner--my informant--sold the
claim, handing over the plant and small staff, our friend the
Zulu remaining to look after the business till the new owner took
possession. In the course of a few months the purchaser became
dissatisfied with his bargain, not a single diamond having turned
up since the transfer. One night the Zulu came to his old master
in a mysterious manner, and laying a handful of diamonds on the
table, said, “There, Baas, are your diamonds; I was not going to
let the new man have any of them!”
CHAPTER II
KIMBERLEY AND ITS DIAMOND MINES
The famous diamond mines in the neighbourhood are Kimberley, De
Beers, Dutoitspan, Bultfontein, and Wesselton (Fig. 2). They
are situated in latitude 28° 43´ South and longitude 24° 46´
East. Kimberley is practically in the centre of the present
diamond-producing area. Besides these mines others of some
importance of the Orange River Colony are known as Jaggersfontein
and Koffyfontein, Lace, and Monastery, besides two new mines, the
Roberts-Victor and the Voorspoed.
The areas of the mines are:
Kimberley 33 acres
De Beers 22 acres
Dutoitspan 45 acres
Bultfontein 36 acres
In 1907 the total number of carats raised from these mines was more
than two million and a half, the sales of which realised £6,452,597.
The most important mine outside the Kimberley group is the new
Premier Mine, about 20 miles West-North-West of Pretoria, where the
famous Cullinan diamond was found.
Other diamond mines are the Frank Smith, Wesselton, the Kamfersdam,
the Kimberley West, the Newlands, and the Leicester Mine.
The surface of the country round Kimberley is covered with a
ferruginous red, adhesive, sandy soil, which makes horse traffic
very heavy. Below the red soil is a basalt, much decomposed and
highly ferruginous, from 20 to 90 feet thick, and lower still
from 200 to 250 feet of black slaty shale containing carbon and
iron pyrites. These are known as the Kimberley shales; they are
very combustible, and in a part of the De Beers Mine where they
were accidentally fired they smouldered for over eighteen months.
Then follows a bed of conglomerate about 10 feet thick, and below
the conglomerate about 400 feet of a hard, compact rock of an
olive colour, called “Melaphyre,” or olivine diabase. Below the
melaphyre is a hard quartzite about 400 feet thick. The strata
are almost horizontal, dipping slightly to the north; in places
they are distorted and broken through by protruding dykes of trap.
There is no water nearer than the Vaal River, about 14 miles away,
and formerly the miners were dependent on rain-water and a few
springs and pools. Now, however, a constant and abundant supply of
excellent water is served to the town, whilst good brick houses,
with gardens and orchards, spring up on all sides. To mark the
rate of progress, Kimberley has an excellent club and one of
the best public libraries in South Africa. Parts of the town,
affectionately called “the camp” by the older inhabitants, are not
beyond the galvanised iron stage, and the general appearance is
unlovely and depressing. Reunert reckons that over a million trees
have been cut down to supply timber for the mines, and the whole
country within a radius of 100 miles has been denuded of wood with
the most injurious effects on the climate. The extreme dryness of
the air, and the absence of trees to break the force of the wind
and temper the heat of the sun, probably account for the dust
storms so frequent in summer. The temperature in the day frequently
rises to 100° in the shade, but in so dry a climate this is not
unpleasant, and I felt less oppressed by this heat than I did in
London the previous September. Moreover, in Kimberley, owing to the
high altitude, the nights are always cool.
The approach to Kimberley is deadly dull. The country is almost
treeless, and the bare veldt stretches its level length, relieved
only by distant hills on the horizon.
THE PIPES OR CRATERS
The five diamond mines or craters are all contained in a circle 3½
miles in diameter. They are irregularly shaped round or oval pipes,
extending vertically downwards to an unknown depth, retaining about
the same diameter throughout (Fig. 3). They are said to be volcanic
necks, filled from below with a heterogeneous mixture of fragments
of the surrounding rocks, and of older rocks such as granite,
mingled and cemented with a bluish-coloured, hard clayey mass, in
which famous blue clay the imbedded diamonds are hidden.
[Illustration: FIG. 3. KIMBERLEY MINE. THE “PIPE.”]
[Illustration: FIG. 4. SECTION OF KIMBERLEY MINE.
To face p. 18.]
The craters or mines are situate in depressions, which have no
outlets for the water which falls upon the neighbouring hills. The
watersheds of these hills drain into ponds, called pans or vleis.
The water, which accumulates in these ponds during the rainy
season, evaporates during the dry months, only one of them holding
water throughout the dry season. The rocks which surround the
craters are capped by red soil or calcareous tufa, and in places by
both, the red soil covering the tufa.
The diamantiferous breccia filling the mines, usually called “blue
ground,” is a collection of fragments of shale, various eruptive
rocks, boulders, and crystals of many kinds of minerals. Indeed,
a more heterogeneous mixture can hardly be found anywhere else
on this globe. The ground mass is of a bluish green, soapy to
the touch and friable, especially after exposure to the weather.
Professor Maskelyne considers it to be a hydrated bronzite with a
little serpentine.
The Kimberley mine is filled for the first 70 or 80 feet with what
is called “yellow ground,” and below that with “blue ground” (Fig.
4). This superposed yellow on blue is common to all the mines.
The blue is the unaltered ground, and owes its colour chiefly to
the presence of lower oxides of iron. When atmospheric influences
have access to the iron it is peroxidised and the ground assumes
a yellow colour. The thickness of yellow earth in the mines
is therefore a measure of the depth of penetration of air and
moisture. The colour does not affect the yield of diamonds.
Besides diamonds, there have been detected more than eighty species
of minerals in the blue ground, the more common being magnetite,
ilmenite, garnet, bright green ferriferous enstatite (bronzite),
a hornblendic mineral closely resembling smaragdite, calc-spar,
vermiculite, diallage, jeffreysite, mica, kyanite, augite, peridot,
eclogite, iron pyrites, wollastonite, vaalite, zircon, chrome
iron, rutile, corundum, apatite, olivine, sahlite, chromite,
pseudobrookite, perofskite, biotite, and quartz. The blue ground
does not show any signs of passing through great heat, as the
fragments in the breccia are not fused at the edges. The eruptive
force was probably steam or water-gas, acting under great pressure,
but at no high temperature. According to Mr. Dunn, in the Kimberley
Mine, at a depth of 120 feet, several small fresh-water shells were
discovered in what appeared to be undisturbed material.
A selection of thin sections of some of these rocks and minerals,
mounted as microscopic objects and viewed by polarised light, are
not only of interest to the geologist, but are objects of great
beauty.
The appearance of shale and fragments of other rocks testify that
the _mélange_ has suffered no great heat in its present condition,
and that it has been erupted from great depths by the agency of
water vapour or some similar gas.
The rock outside the pipes and encasing them is called “reef.”
Inside some of the mines occur large masses of “floating reef,”
covering an area of several thousand square feet. In the De Beers
Mine is what is called “the snake,” a dyke of igneous rock taking a
serpentine course across the mine, and standing like a vein nearly
vertical, varying in thickness from 2 to 7 feet. The main body of
the blue ground is entirely analogous to the snake rock, naturally
more decomposed, but in essential points the microscopic appearance
of the blue ground and of the “snake” is in an extraordinary degree
alike. Mr. Gardner Williams supposes that the “snake” is a younger
eruptive formation coming from the same volcanic source as the blue
ground. No diamonds have been found either in the “snake” or the
floating reef. The ground, however, is generally richer in diamonds
in the neighbourhood of the floating reef.
Before the discovery of the mines there was nothing in the
superficial appearance of the ground to indicate the treasures
below. Since the volcanic ducts were filled with the
diamantiferous ground, denudation has planed the surface and the
upper parts of the craters, and other ordinary signs of volcanic
activity being smoothed away, the superficial and ubiquitous red
sand covered the whole surface. The Kimberley Mine seems to have
presented a slight elevation above the surrounding flat country,
while the sites of other mines were level or even slightly
depressed. The Wesselton Mine, within a mile of Dutoitspan, has
only been discovered a few years. It showed a slight depression
on the surface, which had been used as a shoot for dry rubbish.
There are other diamantiferous pipes in the neighbourhood, but they
are small and do not contain stones in payable quantities. More
recently another diamantiferous pipe has been discovered about
40 miles off, near Klipdam, and is now worked as the Leicester
Mine. Other hoards of diamonds may also be near; where there are
no surface signs, and the pipe itself is hidden under 10 or 20
feet of recent deposits, it is impossible to prospect the entire
country. Accident has hitherto been the chief factor in the
discovery of diamond mines.
How the great pipes were originally formed is hard to say. They
were certainly not burst through in the ordinary manner of volcanic
eruption, since the surrounding and enclosing walls show no signs
of igneous action, and are not shattered or broken up even when
touching the “blue ground.” It is pretty certain these pipes were
filled from below after they were pierced and the diamonds were
formed at some previous time and mixed with a mud volcano, together
with all kinds of debris eroded from the rocks through which it
erupted. The direction of flow is seen in the upturned edges of
some of the strata of shale in the walls, although I was unable to
see any upturning in most parts of the walls of the De Beers Mine
at great depths.
THE KIMBERLEY MINE IN OLD DAYS
According to Mr. Paterson, who examined the diamond fields of
Kimberley soon after their discovery, “Wherever the diamond is
obtained perfect in form and smooth in finest smoothness of
surface, without depression, hump, or twist of any kind, such
diamonds were ever found in their own little moulds of finest
limey stuff,[2] and as if such mould of lime had been a necessity
to their perfect formation. And further, where the splinters of
diamonds, or boarty stuff, were chiefly met by the diggers, there
was much less presence of limey matter in the claim at the section
of it where such broken or fragmentary diamonds were found; and
that chiefly from among what the diggers termed ‘clay-ballast,’ or
‘burnt brick,’ were unearthed the bits or undeveloped crystals so
plentiful at New Rush.”[3]
In the first days of diamond mining there was no idea that
diamantiferous earth extended to any particular depth, and miners
were allowed to dig holes at haphazard and prospect where they
liked. When the Kimberley Mine was discovered a new arrangement was
made, and in July, 1871, it was cut up into about 500 claims, each
31 feet square, with spaces reserved for about fifteen roadways
across the mine. No person at first could hold more than two
claims--a rule afterwards modified.
The following quotation from a description of a visit to Kimberley
in 1872, by Mr. Paterson, taken from a paper read by him to the
Geologists’ Association, gives a graphic picture of the early days
of the Kimberley Mine:
“The New Rush diggings (as the Kimberley Mine was at first called)
are all going forward in an oval space enclosed around by the trap
dyke, and of which the larger diameter is about 1000 feet, while
the shorter is not more than 700 feet in length. Here all the
claims of 31 feet square each are marked out with roadways of about
12 feet in width, occurring every 60 feet. Upon these roadways, by
the side of a short pole fixed into the roadway, sits the owner of
the claim with watchful eye upon the Kafir diggers below, who fill
and hoist, by means of a pulley fixed to the pole above, bucketful
after bucketful of the picked marl stuff in which the diamonds are
found.
“Many of the claims are already sunk to a depth of 100 feet,
and still the diamonds continue to be found as plentifully as
ever. From the roadway above the marl is carted away to the
sorting-tables, outside the range of the diggings, among mounds of
marl stuff which seem like little hills. Here, amidst such whirls
of dust as are nowhere else seen, the marl stuff is pounded, sifted
from the finest powder of lime and clay, and from the residue put
on the sorting-tables, the diggers, with a piece of zinc 9 inches
long by 4 inches in breadth, search out in the successive layers
taken from the heap the precious gems. I need not tell you that
the search is by no means very perfect, or that perhaps as many
diamonds escape the digger’s eye as are discovered and taken out
by him, but you will perhaps confess with me that their aptness
in picking out the diamonds is by no means to be despised, when I
tell you that in one six months from the date of opening New Rush
diggings, little short of a million sterling in diamonds has been
extracted from them. At close of day the diggers take daily stock
of their finds, and between five and six o’clock in the afternoon
are to be seen hundreds and hundreds moving through the main street
of New Rush on visits to the tents of the buyers, seated behind
their little green baize tables, with scales all ready, and bags of
gold and silver and piles of banknotes, to buy the little gems.”
It may help to realise the enormous value of the Kimberley Mine if
I say that two claims, measuring together 62 by 31 feet and worked
to a depth of 150 feet, yielded 28,000 carats of diamonds.
The roadways across the mine soon, however, became unsafe.
Claims were sunk 100 or 200 feet each side of a roadway, and the
temptation to undermine roadways was not always resisted. Falls of
road frequently took place, followed by complete collapse, burying
mine and claims in ruin. At that time there were probably 12,000 or
15,000 men at work in the mine, and then came the difficulty how to
continue working the host of separate claims without interference
with each other. A system of rope haulage was adopted.
The following description of the work at the Kimberley Mine at this
stage of its history is given by Mr. Reunert:[4]
“A succession of tall, massive timber stagings was erected round
the margin of the mine. Each staging carried two or three platforms
one above the other, every platform serving as an independent level
from which to communicate with the claims below. Stationary ropes
were then stretched from the different levels of the stagings to
the claims, the ropes being anchored to the ground at both ends:
the upper platforms communicated with the claims in the centre of
the mine, the lower platforms with those nearer the margin. The
hauling ropes were attached to windlasses worked by Kafirs on the
several platforms, on which grooved guide wheels for the ropes were
also fixed, the buckets being swung from the stationary ropes by
little overhead runners and crooks. Arrived at the level of the
platform the bucket was tipped into a narrow shoot, down which the
ground ran into a bag held ready to receive it, in which it was
conveyed away to be sorted. The din and rattle of these thousands
of wheels and the twang of the buckets along the ropes were
something deafening, while the mine itself seemed almost darkened
by the thick cobweb of ropes, so numerous as to appear almost
touching. This mode of haulage continued in vogue during the whole
of 1873, and if the appearance of the mine was less picturesque
than when the roadways existed, it was, if anything, more unique.
By moonlight, particularly, it was a weird and beautiful sight.”
The mine was now threatened in two other quarters. The removal of
the blue ground took away the support from the walls of the pipe,
and frequent falls of reef occurred, not only covering up valuable
claims with rubbish, but endangering the lives of workers below.
Moreover, as the workings deepened, water made its appearance,
necessitating pumping. In 1878 one quarter of the claims were
covered by reef, and in 1879 over £300,000 were spent on removing
reef and water. In 1881 over £200,000 were thus spent, and in 1882
more than half a million sterling was needed to defray the cost of
reef removal. So matters went on until four million cubic yards
of reef had been removed, at a cost of two millions sterling, and
still little good was done, for out of 400 claims in the mine only
about fifty could be regularly worked. Ultimately, in November,
1883, the biggest fall of reef on record took place, estimated at
250,000 cubic yards, surging half across the mine, where the bulk
of it lies to this day. It became evident that open workings could
not be carried on at such depths, and after many experiments the
present system of underground working was devised.
During this time of perplexity, individual miners who could easily
have worked one or two claims near the surface could not continue
work in the face of harassing difficulties and heavy expenses.
Thus the claims gradually changed hands until the mine became the
property first of a comparatively small number of capitalists, then
of a smaller number of limited liability companies, until finally
the whole of the mines have practically become the property of the
“De Beers Consolidated Mines, Limited.”
CHAPTER III
KIMBERLEY MINES AT THE PRESENT DAY
The De Beers Consolidated Mines, Limited, was founded in 1888,
mainly through the genius of the late Cecil John Rhodes, for the
purpose of acquiring all-important diamond-mining interests in the
Kimberley area and thereby controlling the output. The two richest
mines, Kimberley and De Beers, have been actively worked ever
since, and have been the main contributors to an output which now
realises over five millions sterling annually. Dutoitspan Mine was
completely closed down, and practically the whole of Bultfontein
was kept idle for many years; but with a view to the requirements
of the future and the marked increase in the demand for diamonds,
notwithstanding the steady rise in prices that has taken place,
both these mines have now been equipped for underground working
on a grand scale. The youngest of the De Beers group of mines is
the Wesselton, which was discovered in 1890 by the late Mr. H. A.
Ward, and soon afterwards purchased by Mr. Rhodes on behalf of the
Company. The mine is now being worked opencast on a magnificent
scale and has largely exceeded original expectations (Fig. 5). The
success of the consolidation is proved by the fact that since it
was brought about £22,000,000 have been paid in dividends to the
shareholders, and it is roughly estimated that 40,000,000 carats of
diamonds have been produced of a total value of eighty millions.
[Illustration: FIG. 5. WESSELTON DIAMOND MINE. OPEN WORKINGS.
To face p. 34.]
At the four mines about 8000 persons are daily employed, namely,
1500 whites and 6500 blacks. The wages are, whites, £5 or £6 a
week; blacks, underground, 4s. to 5s. a day, and aboveground, 21s.
a week.
THE COMPOUND SYSTEM
With gems like diamonds, where so large an intrinsic value is
concentrated into so small a bulk, it is not surprising that
robbery has to be guarded against in the most elaborate manner. The
Illicit Diamond Buying (I.D.B.) laws are very stringent, and the
searching, rendered easy by the “compounding” of the natives--which
I shall describe presently--is of the most drastic character (Fig.
6). It is, in fact, very difficult for a native employee to steal
diamonds; even were he to succeed, it would be almost impossible to
dispose of them, as a potential buyer would prefer to secure the
safe reward for detecting a theft rather than run the serious risk
of doing convict work on the Cape Town Breakwater for a couple of
years. I heard of a native who, secreting a diamond worth several
hundreds of pounds, after trying unsuccessfully to sell it, handed
it back to the manager of his compound, glad to get the sixpence a
carat to which he was entitled. Before the passing of the “Diamond
Trade Act” the value of diamonds stolen reached nearly one million
sterling per annum.
A “compound” is a large enclosure about 20 acres in extent,
surrounded by rows of one-story buildings of corrugated iron.
These are divided into rooms holding each about twenty natives. A
high iron fence is erected around the compound, 10 feet from the
buildings. Within the enclosure is a store where the necessaries
of life are supplied to the natives at a reduced price, wood and
water being provided free of charge. In the middle is a large
swimming-bath, with fresh water running through it. The rest of
the space is devoted to recreation, games, dances, concerts, and
any other amusement the native mind can desire. I have to thank
the superintendents of the respective compounds, who spoke all
the native dialects, for their kindness in showing us round, and
suggesting dances and concerts, got up at ten minutes’ notice, for
the benefit of my camera. The dancing was more of the character
of attitudinising and marching to a monotonous tum-tum, the
“orchestra” consisting of various-sized drums and what they call
a piano--an octave or so of tuned slabs of wood held in order on
stretched strings and struck with a wooden hammer. The native music
as a rule is only marking time, but I have heard musical melodies
accompanying some of their songs. In case of accident or illness
there is a well-appointed hospital where the sick are tended.
Medical supervision, nurses, and food are supplied free by the
Company.
In the compound are to be seen representatives of nearly all the
picked types of African tribes. Each tribe keeps to itself, and
to go round the buildings skirting the compound is an admirable
object-lesson in ethnology. At one point is a group of Zulus; next
we come to Fingoes; then Basutos; beyond come Matabele, Bechuanas,
Pondos, Shangains, Swazis, and other less-known tribes, either
grouped or wandering around making friendly calls.
The clothing in the compound is diverse and original. Some of the
men are evident dandies, whilst others think that in so hot a
climate a bright-coloured handkerchief or “a pair of spectacles
and a smile” is as great a compliance with the conventions of
civilisation as can be expected.
The natives are not interfered with in their various amusements,
always provided they do not make themselves objectionable to their
neighbours. They soon learn that tribal animosities are to be left
outside the compound. One Sunday afternoon my wife and I walked
unattended about the compound, almost the only whites present among
1700 natives. The manners of the fold were so friendly, and their
smiles so cordial, that the idea of fear vanished. At one part a
Kafir was making a pair of trousers with a bright nickel-plated
sewing-machine, in which he had invested his savings; next to him
a “boy” was reading from the Testament in his own language to an
attentive audience; in a corner a party were engaged in cooking a
savoury mess in an iron pot; further on the orchestra was tuning
up and Zulus were putting the finishing touches to their toilet of
feathers and beads. One group was intently watching a mysterious
game. It is played by two sides, with stones and grooves and
hollows in the ground, and appears of most absorbing interest. It
seems to be universal throughout Africa; it is met with among the
ruins of Zimbabwe, and signs of it are recorded on old Egyptian
monuments. I wanted to learn it, and an intelligent Zulu player
offered to teach it to me in a few minutes. Captain Dallas,
however, with a more accurate opinion of my intelligence than my
friend the Zulu, assured me it would take months before I could
begin to know anything about it. He had tried for years and could
make nothing of it.
[Illustration: FIG. 6. DE BEERS COMPOUND.]
[Illustration: FIG. 7. DE BEERS MINE. UNDERGROUND WORKINGS.
To face p. 40.]
They get good wages, varying according to occupation. The work
is appreciated, and there are always more applicants than can be
accepted. On entering, the restrictions to which they must submit
are fully explained, and they are required to sign for three months
at least, during which time they must not leave the compound or
mine. A covered way and tunnel lead the workers underground to the
down shaft, while those working on the depositing floors go and
come under guard. It is seldom that a man does not return once he
has lived the life in the compound; some come again and again for
years, only leaving occasionally to spend accumulated savings.
The most careful men save money, and carry it at intervals to the
superintendent to keep for them. Occasionally they ask to look
at their savings, which may amount to £30 or £40, accumulated
by driblets. They are ignorant of savings banks or interest, and
are content if they see their own money in the original rags and
papers. The Kafir, on demand, must behold his coins just as he
handed them in, wrappings and all. Sometimes the superintendent
will have as much as £1000 of savings in his care.
On leaving, the men generally draw all their savings, and it is not
uncommon for a grateful Kafir to press £2 or £3 on Captain Dallas
in recognition of his trouble. They are astonished when their
offerings are declined; still more so when it is explained that if
they would put their savings in a bank they would have a few extra
pounds given to them for the privilege of taking care of it.
A shrewd young Pondo, who had been coming year after year, applied
for some of his savings, and gave as a reason that he wanted to buy
a wife. “But you said the same thing last year,” replied Captain
Dallas; “I hope nothing has happened.” “No,” said the man; “one
wife, she quarrel with me; two wives, they quarrel with each other;
me peace!”
UNDERGROUND WORKINGS
In the face of constant developments I can only describe the system
in use at the time of my own visits in 1896 and 1905. Shafts are
sunk in the solid rock at a sufficient distance from the pipe to
be safe against reef movements in the open mine. In 1903 the rock
shafts in the De Beers and Kimberley Mines reached depths of 2076
and 2599 feet respectively. Tunnels are driven from these shafts
at different levels, about 120 feet apart, to cross the mine from
west to east. These tunnels are connected by two other tunnels
running north and south, one near the west side of the mine and one
midway between it and the east margin of the mine. From the east
and west tunnels offsets are driven to the surrounding rock. When
near the rock the offsets widen into galleries, these in turn being
stoped on the sides until they meet, and upwards until they break
through the blue ground. The fallen reef with which the upper part
of the mine is filled sinks and partially fills the open space. The
workmen then stand on the fallen reef and drill the blue ground
overhead, and as the roof is blasted back the debris follows. When
stoping between two tunnels the blue is stoped up to the debris
about midway between the two tunnels. The upper levels are worked
back in advance of the lower levels, and the works assume the
shape of irregular terraces. The main levels are from 90 to 120
feet apart, with intermediate levels every 30 feet. Hoisting is
done from only one level at a time through the same shaft. By this
ingenious method every portion of blue ground is excavated and
raised to the surface, the rubbish on the top gradually sinking and
taking its place.
The scene below ground in the labyrinth of galleries is bewildering
in its complexity, and very unlike the popular notion of a diamond
mine (Fig. 7). All below is dirt, mud, grime; half-naked men, dark
as mahogany, lithe as athletes, dripping with perspiration, are
seen in every direction, hammering, picking, shovelling, wheeling
the trucks to and fro, keeping up a weird chant which rises in
force and rhythm when a greater task calls for excessive muscular
strain. The whole scene is more suggestive of a coal mine than a
diamond mine, and all this mighty organisation, this strenuous
expenditure of energy, this costly machinery, this ceaseless toil
of skilled and black labour, goes on day and night, just to win a
few stones wherewith to deck my lady’s finger! All to gratify the
vanity of woman! “And,” interposed a lady who heard this remark,
“the depravity of man!”
THE DEPOSITING FLOORS
Owing to the refractory character of blue ground fresh from the
mines, it has to be exposed to atmospheric influences before it
will pulverise under the action of water and mechanical treatment.
From the surface-boxes, into which the blue ground is tipped
when it reaches the top of the main shaft, it is transferred to
side-tipping trucks and sent to the depositing floors by means of
endless wire-rope haulage. The speed of the haulage varies from 2½
to 4 miles per hour. The trucks are counted automatically as they
are sent to the floor by a reciprocating engine-counter placed on
a frame near the tramline.
The depositing floors are prepared by removing the bush and
grass from a fairly level piece of ground; this ground is then
rolled smooth and hard. The floors extend over many square miles
of country and are surrounded by 7-foot barbed wire fences,
vigilantly guarded day and night. The De Beers floors, on
Kenilworth, are laid off in rectangular sections 600 yards long and
200 yards wide, each section holding about 50,000 loads. The ground
from the Kimberley Mine is the softest and only needs a few months’
exposure on the floors; the ground from De Beers is much harder and
requires at least six months’ exposure, while some ground is so
hard that it will not disintegrate by exposure to the weather under
one or two years. The De Beers Mine contains a much larger quantity
of this hard blue ground than the other mines, and in order to save
the loss of time consequent on keeping an enormous stock of blue
constantly on the floors, it has recently been decided to pass
the harder and more refractory stuff direct from the mine through
crushing mills.
For a time the blue ground remains on the floors without undergoing
much alteration. But soon the heat of the sun and moisture produce
a wonderful effect. Large pieces, hard as ordinary sandstone when
taken from the mine, commence to crumble. At this stage the winning
of the diamonds assumes more the nature of farming than mining.
The ground is frequently harrowed and occasionally watered, to
assist pulverisation by exposing the larger pieces to atmospheric
influences. The length of time necessary for the ground to weather
before it becomes sufficiently pulverised for washing depends on
the season of the year and the amount of rain. The longer the
ground remains exposed the better it is for washing.
[Illustration: FIG. 8. DE BEERS WASHING AND CONCENTRATING MACHINERY.
To face p. 48.]
It is curious to note that there is a marked difference in the
rapidity of disintegration of the blue ground in each of the four
mines. The longer the exposure, the more complete the pulverisation
and the better for washing. Under normal conditions soft blue
ground becomes sufficiently pulverised in from four to six
months, but it is better to expose it for a longer period, even for
a whole year.
WASHING AND CONCENTRATING MACHINERY
After the blue ground has been weathered for a sufficient time, it
is again loaded into trucks and hauled to the crushing machinery
(Fig. 8). The first or “comet” crushers reduce the ground so that
it will pass into hoppers and thence into revolving cylinders
covered with perforated steel plates, having holes 1¼ inches in
diameter which separate the finely crushed from the coarse pieces.
Pieces larger than 1¼ inches pass out of the end of the cylinders
and fall upon a conveyor belt, which takes them to the end of the
machine--these pieces are mostly waste rock which is found in the
blue ground.
The fine ground which passes through the holes in the cylinder,
together with a plentiful current of water, flows into the washing
pans. These pans are of iron, 14 feet in diameter, furnished with
ten arms each having six or seven teeth. The teeth are so set as
to form a spiral, so that when the arms revolve the teeth carry
the heavy deposit to the outer rim of the pan, while the lighter
material passes towards the centre and is carried from the pan
by the flow of water. The heavy deposit contains the diamonds.
It remains on the bottom of the pan and near its outer rim. This
deposit is drawn off every twelve hours by means of a broad slot
in the bottom of the pan. The average quantity of blue ground
passed through each pan is from 400 to 450 loads in ten hours. The
deposit left in each pan after putting the above number of loads
through amounts to three or four loads, which go to the pulsator
for further concentration.
About 14 per cent of all the ground sent to the depositing floors
is too hard to weather, so of late years crushing and concentrating
plant has been erected to deal effectually with the hard lumps,
thus saving the great lock-up of capital consequent on letting them
lie on the floor a year or two.
The hard lumps being hauled to the upper part of the machine,
are tipped into bins, whence they pass to crushing rollers which
so reduce them that they will pass through a ring two inches in
diameter. The coarse powder is screened through revolving cylinders
having ½-inch and 1¼-inch perforations. The stuff passing through
the finer holes goes to the finishing mill, while the coarser stuff
goes to smaller crushers. Before the coarse lumps are re-crushed
they pass over revolving picking tables, where any specially large
diamonds are rescued, thus preventing the risk of breakage. From
the picking tables the ground is scraped automatically into two
sets of rolls, and the pulverised product screened again and graded
into three sizes. The finest size, passing a ½-inch screen, goes
to the washing pans, and the two coarser sizes to jigs. Large
diamonds which have been separated from their envelope of blue are
retained in the jig. The ground still holding the smaller diamonds
passes out of the end of the jig and then through a series of
rolls, screens, and jigs until the diamantiferous gravel is drawn
from the bottom jigs into locked trucks running on tramways to the
pulsator for further concentration and sorting.
The pulsator is an ingeniously designed but somewhat complicated
machine for dealing with the diamantiferous gravel already reduced
one hundred times from the blue ground, the pulsator still further
concentrating it till the gravel is rich enough to enable the
stones to be picked out by hand. The value of the diamonds in a
load of original blue ground being about 30s., the gravel sent
to the pulsator from the pans, reduced a hundredfold, is worth
£150 a load. Stuff of this value must not be exposed to risk of
peculation.
The locked trucks are hoisted by a cage to a platform, where they
are unlocked and their contents fed into a shoot leading to a
cylinder covered with steel sieving with holes from 1/16 to ⅝ of an
inch in diameter. The five sizes which pass through the cylinder
flow upon a combination of jigs, termed at the mines the pulsators.
The bottoms of the jigs are covered with screens, or sieving, the
meshes of which are a little larger than the holes in the revolving
cylinder immediately at the back of them.
Over each screen is spread a layer of bullets to prevent the
rich deposit from passing too rapidly through the screens. The
jigs themselves are stationary, but from below an intermittent
stream of water passes in rapid pulsations with an up and down
movement. This pulsation keeps the diamantiferous gravel constantly
moving--“alive” is the expressive word used--and tends to sort out
the constituents roughly according to their specific gravity, the
heavier particles working to the bottom and the lighter material
washing off by the flow of water and passing into trucks, whence
it is carried to the tailings heap. The heavier portions, by the
up and down wash of the water, gradually work their way under the
bullets and pass through the screens into pointed boxes, whence
the heavy concentrates are drawn off upon endless belts. These
convey their precious load to small elevators by means of which the
concentrates are lifted into hoppers from which they are fed upon
shaking tables.
[Illustration: FIG. 9. SORTING CONCENTRATES FOR DIAMONDS. DE BEERS.
To face p. 54.]
CHAPTER IV
COLLECTING THE GEMS
The sorting room in the pulsator house is long, narrow, and
well lighted (Fig. 9). Here the rich gravel is brought in wet,
a sieveful at a time, and is dumped in a heap on tables covered
with iron plates. The tables at one end take the coarsest lumps,
next comes the gravel which passed the ⅜-inch holes, then the
next in order, and so on. The first sorting is done by thoroughly
trustworthy white men; for here the danger of robbery is greatest.
Sweeping the heap of gravel to the right, the sorter scrapes a
little of it to the centre of the table by means of a flat piece of
sheet zinc. With this tool he rapidly passes in review the grains,
seizes the diamonds and puts them into a little tin box in front
of him. The stuff is then swept off to the left and another lot
taken, and so on till the sieveful of gravel is exhausted, when
another is brought in. The stuff the sorter has passed to his left
as temporarily inspected is taken next to another part of the room,
where it is again scrutinised by native convicts again and again,
and whilst diamonds can be found in quantity sufficient to repay
the cost of convict labour, it is passed under examination.
The diamond has a peculiar lustre, and on the sorter’s table it is
impossible to mistake it for any other stone that may be present.
It looks somewhat like clear pieces of gum arabic, with a sort of
intrinsic lustre which makes a conspicuous shine among the other
stones.
AUTOMATIC DIAMOND COLLECTOR
A series of experiments was initiated by Mr. Gardner Williams with
the object of separating the diamonds from the heavy, valueless
concentrates with which they are associated. An ordinary shaking
or percussion table was constructed, and every known means of
separation was tried without success. One of the employees of De
Beers, Mr. Fred Kirsten, was in charge of the experimenting, under
the supervision of the late Mr. George Labram, the manager of the
large crushing plant, and afterwards mechanical engineer to the
Company. Notwithstanding the fact that the specific gravity of
the diamond (3·52) was less than that of several of the minerals
associated with it, so that its separation would seem a simple
matter, it was found in practice to be impossible owing to the
slippery nature of the diamond. The heavy concentrates carried
diamonds, and diamonds flowed away from the percussion table with
the tailings. When it seemed that every resource to do away with
hand-sorting had been exhausted, Kirsten asked to be allowed to
try to catch the diamonds by placing a coat of thick grease on the
surface of the percussion table with which the other experiments
had been made. Kirsten had noticed that oily substances, such as
axle grease and white or red lead, adhered to diamonds when they
chanced to come into contact, and, he argued to himself, if these
substances adhered to diamonds and not to the other minerals in
the concentrates, why should not diamonds adhere to grease on the
table and the other minerals flow away? In this way the remarkable
discovery was made that diamonds alone of all minerals contained
in the blue ground will adhere to grease, and that all others will
flow away as tailings over the end of the percussion table with
the water. After this was determined by thorough experiments,
more suitable shaking tables were constructed at the Company’s
workshops. These were from time to time improved upon, until now
all the sorting (except for the very coarse size) is done by these
machines, whose power of distinction is far superior to the
keenest eye of the native.
Only about ⅓ of 1 per cent of diamonds is lost by the first table,
and these are recovered almost to a stone when the concentrates are
passed over the second table. The discrimination of this sorter
is truly marvellous. Native workers, although experienced in the
handling of diamonds, often pick out small crystals of zircon, or
Dutch boart, by mistake, but the senseless machine is practically
unerring.
The grease containing the diamonds, together with a small
percentage of very heavy minerals, such as iron pyrites and
barytes, is scraped from the tables, placed in buckets made of
steel plates with fine perforations, and boiled or steamed. The
grease passes away to tanks of water, where it is cooled and is
again fit for use. The diamonds, together with small bits of iron
pyrites, brass nails from the miners’ boots, pieces of copper
from the detonator used in blasting, which remain on the tables
owing to their high specific gravity, and a very small admixture
of worthless deposit which has become mechanically mixed with the
grease, are then boiled in a solution containing caustic soda,
where they are freed from all grease. The quantity of deposit from
the size of ⅝ of an inch downwards, which now reaches the sorting
table, does not exceed 1 cubic foot for every 12,000 loads (192,000
cubic feet) of blue ground washed. As already stated, 5/12 of 1
per cent of the whole mass of blue formerly passed to the sorting
tables; or, from 12,000 loads, which is about the daily average of
the quantity washed at De Beers and Kimberley Mines, 800 cubic feet
had to be assorted by hand.
THE YIELD OF DIAMONDS
Sometimes as many as 8000 carats of diamonds come from the pulsator
in one day, representing about £20,000 in value.
When the bare statement is made that nearly 5,000,000 truck-loads,
or more than 4,000,000 tons of blue ground, have been washed in a
year, the mind only faintly conceives the prodigious size of the
mass that is annually drawn from the old craters and laboriously
washed and sorted for the sake of a few bucketfuls of diamonds. It
would form a cube of more than 430 feet, or a block larger than any
cathedral in the world, and overtopping the spire of St. Paul’s,
while a box with sides measuring 2 feet 9 inches would hold the
gems. From two to three million carats of diamonds are turned out
of the De Beers mines in a year, and as 5,000,000 carats go to the
ton, this represents half a ton of diamonds. To the end of 1892 10
tons of diamonds had come from this mine, valued at £60,000,000
sterling. This mass of blazing diamonds could be accommodated in a
box 5 feet square and 6 feet high.
The diamond is a luxury, and there is only a limited demand
for it throughout the world. From four to four and a half
millions sterling is as much as is spent annually in diamonds;
if the production is not regulated by the demand, there will be
over-production, and the trade will suffer. By regulating the
output the directors have succeeded in maintaining prices since the
consolidation in 1888.
The blue ground varies in its yield of diamonds in different mines,
but is pretty constant in the same mine. In 1890 the yield per load
of blue ground was:
CARATS
From the Kimberley Mine from 1·25 to 1·5
” De Beers Mine ” 1·20 ” 1·3
” Dutoitspan Mine ” 0·17 ” 0·5
” Bultfontein Mine ” 0·5 ” 0·33
VARIETIES OF DIAMONDS
FANCY STONES
Diamonds occur in all shades, from deep yellow to pure white and
jet black, from deep brown to light cinnamon, also green, blue,
pink, yellow, orange, and opaque.
Both in Kimberley and De Beers the blue ground on the west side
is poorer in diamonds than the blue ground in other parts of the
mines. The diamonds from the west side also differ somewhat from
those in other parts of the same mine.
The diamonds from each mine have a distinctive character, and so
uniform are the characteristics that an experienced buyer can
tell at once the locality of any particular parcel of stones. An
isolated stone may, of course, be found occasionally in any one
mine which is characteristic of some other source of production,
but this is the exception to the general rule.
There is a great similarity between the produce of the De Beers and
Kimberley mines. A day’s wash from either of these mines could be
distinguished from each other, but not so easily the majority of
the individual stones.
The Kimberley Mine produces a small percentage of white crystals,
octahedral in shape, is noted for its large macles, and, in common
with the De Beers Mine, it also yields a large percentage of
coloured and large yellow diamonds.
The De Beers Mine produces a comparatively small percentage of
really white diamonds, but is noted for its fine silvery capes.
The Dutoitspan Mine is noted for its fine white cleavages, silver
capes, large yellows, and an exceptional proportion of large stones
generally. It also produces a small proportion of fine white,
octahedral-shaped crystals and a comparatively small proportion of
diamonds below 0·2 of a carat in size.
The Bultfontein Mine produces a very large percentage of white
diamonds, mostly octahedral in shape and generally small in size.
It produces very few coloured stones, but a larger percentage of
flawed and spotted stones than any other mine. Even the apparently
pure stones from this mine frequently develop flaws in cutting,
which in the rough were imperceptible to the naked eye.
The Wesselton Mine diamonds are noted for an abnormally large
percentage of octahedral stones, a large proportion of which are
free from flaws. White and brown stones predominate in this mine;
there is almost an entire absence of the ordinary yellow, but very
fine golden-coloured fancy stones are unearthed occasionally,
invariably in the form of cleavage, and hardly ever exceeding 2
carats each in weight.
For “golden fancies” this mine is unrivalled. Wesselton diamonds
are easily distinguished from the produce of every other mine by a
decided gloss common to them.
Wesselton produces more stones of 10 carats each and over than
Bultfontein, but comparatively few large stones of over 50 carats
each. It produces a very large percentage of small diamonds under
0·2 of a carat. With Bultfontein it shares the distinction of
yielding cubical stones occasionally. It also produces a small
percentage of blue-whites.
The Frank Smith Mine produces very fine white diamonds, fairly
regular in shape, mostly octahedral, and hardly any coloured
stones. Many of the stones are grooved at the edges.
The Kamfersdam Mine yields diamonds of very inferior quality, dark
brown being the predominating colour, and even the majority of the
better-class stones from this mine are faintly tinged with brown.
The Kimberley West, formerly known as Theron’s Mine, situated about
30 miles due west of Kimberley, yields a very small percentage of
blue-whites, fine “silver capes,” and a large proportion of brown
diamonds, somewhat better in quality than Kamfersdam and more
regular in shape. The diamonds from this mine present a distinctly
“alluvial” appearance, but they are nevertheless distinctive in
character from river diamonds and much inferior in quality.
The diamonds from the Leicester Mine are of a distinctive
character; they are very much grooved, extremely bad shapes for
cutting, and many of the stones are cross-grained.
The Newlands Mine, West Griqualand, about 40 miles north-west
of Kimberley, is interesting on account of the occurrence of
diamond in what the Reverend Professor Bonney considers to be its
true matrix. The workmen occasionally come across well-rounded,
boulder-like masses of eclogite, a rather coarsely crystalline
rock, sometimes more than a foot in diameter. Some of these
boulders have diamonds imbedded in them. One piece examined by
Professor Bonney measured approximately 4 inches by 3 inches by
2 inches, and appeared to have been broken off a larger eclogite
boulder. In it were seen ten diamonds, mostly well-crystallised
octahedra, perfectly colourless, with brilliant lustre, four of
them being comprised within a space of a quarter of an inch square.
All these diamonds were on the surface. Probably others would have
been found inside, but it was not considered desirable to destroy
the specimen by breaking it up. It is now in the Natural History
Museum, having been presented by the Directors of the Newlands Mine.
Eclogite has been found in other diamond mines, but I am not aware
that diamonds have been found imbedded in it except in the Newlands
Mine.
Stones from Jagersfontein, in the Orange River Colony, display
great purity of colour and brilliancy, and they have the so-called
“steely” lustre characteristic of old Indian gems.
FALLING OFF OF YIELD WITH DEPTH
According to tables furnished by the De Beers Company, the yield
of the De Beers and Kimberley mines has declined as the depth
increases. At the same time the value of the stones has risen, and
diamonds are more expensive to-day than at any previous time.
NUMBER OF VALUE
YEAR CARATS[5] PER CARAT
PER LOAD _s._ _d._
1889 1·283 19 8·75
1890 1·15 32 6·75
1891 0·99 29 6
1892 0·92 25 6
1893 1·05 29 0·6
1894 0·89 24 5·2
1895 0·85 25 6
1896 0·91 26 9·4
1897 0·92 26 10·6
1898 0·80 26 6·2
1899 0·71 29 7·2
1900 0·67 35 10·2
1901 0·76 39 7
1902 0·76 46 5·7
1903 0·61 48 6·3
1904 0·54 48 11·8
STONES OTHER THAN DIAMONDS
Accompanying diamonds in the concentrates are a number of other
minerals of high specific gravity, and some of notable beauty.
Among these are the rich red pyrope (garnet), sp. gr. 3·7,
containing from 1·4 to 3 per cent of oxide of chromium; zircon,
in flesh-coloured grains and crystals, sp. gr. 4 to 4·7; kyanite,
sp. gr. 3·45 to 3·7, discernible by its blue colour and perfect
cleavage; chrome diopside, sp. gr. 3·23 to 3·5, of a bright green
colour; bronzite, sp. gr. 3·1 to 3·3; magnetite, sp. gr. 4·9 to
5·2; mixed chrome and titanium iron ore, sp. gr. 4·4 to 4·9,
containing from 13 to 61 per cent of oxide of chromium, and from
3 to 68 per cent of titanic acid, in, changeable quantities;
hornblende, sp. gr. 2·9 to 3·4; barytes, sp. gr. 4·3 to 4·7; and
mica. Some of the garnets are of fine quality, and one was recently
cut which resembled a pigeonblood ruby, and attracted an offer of
£25.
In the pulsator and sorting house most of the native labourers
are long-sentence convicts, supplied with food, clothing, and
medical attendance by the Company. They are necessarily well
guarded. I myself saw about 1000 convicts at work. I was told that
insubordination is very rare; apart from the hopelessness of a
successful rising, there is little inducement to revolt; the lot
of these diamond workers is preferable to life in the Government
prisons, and they seem contented.
[Illustration: FIG. 10. DE BEERS DIAMOND OFFICE. 25,000 CARATS.]
[Illustration: FIG. 11. DE BEERS DIAMOND OFFICE. THE VALUATORS’
TABLE.
To face p. 72.]
CHAPTER V
THE DIAMOND OFFICE
From the pulsator the diamonds are sent to the general office
in Kimberley to be cleansed in a boiling mixture of nitric and
sulphuric acids. A parcel of diamonds loses about half a part per
1000 by this treatment. On one of my visits to the diamond office
the door opened and in walked two young men, each carrying a large
enamelled saucepan containing something steaming hot. They went to
one of the zinc-covered tables and turned out from the saucepans a
lustrous heap of 25,000 carats of diamonds (Fig. 10). They had just
been boiled in acid and washed.
After purification the diamonds are handed to the valuators (Fig.
11), who sort them into classes, according to size, colour, and
purity. In the diamond office they are sorted into ten classes. In
the year 1895, in 1141·8 carats of stones, the proportions of the
different classes were as follows:
Close goods (best stones) 53·8
Spotted stones 75·8
Fine cleavage 79·1
Flats 39·5
Macles 36·5
Ordinary and rejection cleavage 243·4
Rejection stones 43·2
Light and brown cleavage 56·9
Rubbish 371·8
------
1000·0
------
Fine sand 141·8
------
1141·8
It is a sight for Aladdin to see the valuators at work in the
strong-room of the De Beers Company at Kimberley. The tables are
literally heaped with stones won from the rough blue ground--stones
of all sizes, purified, flashing, and of inestimable price; stones
that will be coveted by men and women all the world over; and
last, but not least, stones that are probably destined to largely
influence the development and history of a whole huge continent.
CHAPTER VI
NOTEWORTHY DIAMONDS
Prodigious diamonds are not so uncommon as is generally supposed.
Diamonds weighing over an ounce (151·5 carats) are not unfrequent
at Kimberley. Some years ago, in one parcel of stones, I saw eight
perfect ounce crystals, and one stone weighing 2 ounces (Fig.
12). The largest diamond from the Kimberley mines weighed 428½
carats, or nearly 4 ounces troy. It measured 1⅞ inch through the
longest axis and was 1½ inch square. After cutting it weighed 228½
carats, losing 200 carats in the process. The largest known diamond
was discovered in January, 1905, at the New Premier Mine, near
Pretoria. This mine is of the same type as the Kimberley mines, but
larger in size, and, in fact, is the largest known diamantiferous
pipe in the world--the pipe containing the “blue ground,” along
the longer diameter of its oval-shaped cross-section, measuring
over half a mile, and its area is estimated at 350,000 square
yards. This pipe breaks through felsitic rocks. The diamond, called
“Cullinan” from the name of one of the directors of the company
on whose farm it was discovered, was presented to King Edward on
his birthday by the people of the Transvaal. It weighed no less
than 3025¾ carats, or 9586·5 grains (1·37 lb. avoirdupois). It was
a fragment, probably less than half, of a distorted octahedral
crystal; the other portions still await discovery by some fortunate
miner. The frontispiece shows this diamond in its natural size,
from a photograph taken by myself. I had an opportunity of
examining and experimenting with this unequalled stone before it
was cut. A beam of polarised light passed in any direction through
the stone, and then through an analyser, revealed colours in all
cases, appearing brightest when the light passed along the greatest
diameter--about 4 inches. Here the colours were very fine, but
no regular figure was to be seen. Round a small black spot in
the interior of the stone the colours were very vivid, changing
and rotating round the spot as the analyser was turned. These
observations indicated internal strain.
[Illustration: FIG. 12. A GROUP OF LARGE DIAMOND CRYSTALS.
To face p. 76.]
The clearness throughout was remarkable, the stone being absolutely
limpid like water, with the exception of a few flaws, dark
graphitic spots, and coloured patches close to the outside. At one
part near the surface there was an internal crack, showing well
the colours of thin plates. At another point there was a milky,
opaque mass, of a brown colour, with pieces of what looked like
iron oxide. There were four cleavage planes of great smoothness and
regularity. On other parts of the surface the crystalline structure
was very marked. The edges were rounded in parts, and triangular
markings (depressions) were to be seen. I also noticed square
depressions, nearly as sharp and perfect as the triangular ones.
The cleaving and cutting and polishing of the Cullinan diamond
was entrusted to the firm of Asscher and Co., in Amsterdam. The
cleavage of the diamond was very successfully accomplished by Mr.
Joseph Asscher. An incision half an inch deep was made with a sharp
diamond point in the proper place, then a specially designed knife
blade was placed in the incision and it was struck a heavy blow
with a piece of steel. The diamond split through a defective spot,
part of which was left in each portion of the diamond.
Gigantic as is the Cullinan diamond, it represents in weight less
than half the daily output of the De Beers mines, which averages
about 7000 carats per day.
Next in size to the Cullinan comes the one which was found at the
Jagersfontein Mine. It weighed 970 carats--over half a pound.
The following table gives the names and weights of some historic
diamonds (Fig. 13):
1. Koh-i-noor, after the second cutting, 106 carats.
2. Loterie d’Angleterre, 49 carats.
3. Nizam of Hyderabad, 279 carats.
4. Orloff, 194 carats.
5. Koh-i-noor, after first cutting, 279 carats.
6. Regent or Pitt, 137 carats.
7. Duke of Tuscany, 133 carats.
8. Star of the South, 124 carats.
9. Pole Star, 40 carats.
10. Tiffany, yellow, 125 carats.
11. Hope, blue diamond, 44 carats.
12. Sancy, 53 carats.
13. Empress Eugenie, 51 carats.
14. Shah, 86 carats.
15. Nassak, 79 carats.
16. Pasha of Egypt, 40 carats.
17. Cullinan, 3025 carats.
18. Excelsior, Jagersfontein, 969 carats.
[Illustration: FIG. 13. SOME HISTORIC DIAMONDS.
To face p. 80.]
CHAPTER VII
BOART, CARBONADO, AND GRAPHITE
The black inclusions in some transparent diamonds consist of
graphite. On crushing a clear diamond showing such spots and
heating in oxygen to a temperature well below the point at which
diamond begins to burn, Moissan found that the grey tint of the
powder disappeared, no black spots being seen under the microscope.
There also occur what may be considered intermediate forms between
the well-crystallised diamond and graphite. These are “boart” and
“carbonado.” Boart is an imperfectly crystallised diamond, having
no clear portions, and therefore useless for gems. Shot boart is
frequently found in spherical globules, and may be of all colours.
Ordinary boart is so hard that it is used in rock-drilling,
and when crushed it is employed for cutting and polishing other
stones. Carbonado is the Brazilian term for a still less perfectly
crystallised form of carbon. It is equally hard, and occurs in
porous masses and in massive black pebbles, sometimes weighing two
or more ounces.
The ash left after burning a diamond invariably contains iron as
its chief constituent; and the most common colours of diamonds,
when not perfectly pellucid, show various shades of brown and
yellow, from the palest “off colour” to almost black. These
variations give support to the theory advanced by Moissan that
the diamond has separated from molten iron--a theory of which I
shall say more presently--and also explain how it happens that
stones from different mines, and even from different parts of the
same mine, differ from each other. Further confirmation is given
by the fact that the country round Kimberley is remarkable for
its ferruginous character, and iron-saturated soil is popularly
regarded as one of the indications of the near presence of diamonds.
GRAPHITE
Intermediate between soft carbon and diamond come the graphites.
The name graphite is given to a variety of carbon, generally
crystalline, which in an oxidising mixture of chlorate of potassium
and nitric acid forms graphitic oxide. This varies in colour
from green to brown or yellow, or it is almost without colour,
according to the completeness of the reaction. Graphites are of
varying densities, from 2·0 to 3·0, and generally of crystalline
aspect. Graphite and diamond pass insensibly into one another. Hard
graphite and soft diamond are near the same specific gravity. The
difference appears to be one of pressure at the time of formation.
Some forms of graphite exhibit the remarkable property by which
it is possible to ascertain approximately the temperature at
which they were formed, or to which they have subsequently been
exposed. Sprouting graphite is a form, frequently met with in
nature, which on moderate heating swells up to a bulky, very
light mass of amorphous carbon. Moissan has found it in blue
ground from Kimberley; my own results verify his. When obtained by
simple elevation of temperature in the arc or the electric furnace
graphites do not sprout; but when they are formed by dissolving
carbon in a metal at a high temperature and then allowing the
graphite to separate out on cooling, the sprouting variety appears.
The phenomenon of sprouting is easily shown. If a few grains are
placed in a test-tube and heated to about 170° C., the grains
increase enormously in bulk and fill the tube with a light form of
amorphous carbon.
The resistance of a graphite to oxidising agents is greater the
higher the temperature to which it has previously been exposed.
Graphites which are easily attacked by a mixture of fuming nitric
acid and potassium chlorate are rendered more resistant by strong
heat in the electric furnace.
I have already signified that there are various degrees of
refractoriness to chemical reagents among the different forms of
graphite. Some dissolve in strong nitric acid; other forms of
graphite require a mixture of highly concentrated nitric acid and
potassium chlorate to attack them, and even with this intensely
powerful agent some graphites resist longer than others. M. Moissan
has shown that the power of resistance to nitric acid and potassium
chlorate is in proportion to the temperature at which the graphite
was formed, and with tolerable certainty we can estimate this
temperature by the resistance of the specimen of graphite to this
reagent.
CRYSTALLISATION
The diamond belongs to the isometric system of crystallography; the
prevailing form is octahedral. It frequently occurs with curved
faces and edges. Twin crystals (macles) are not uncommon. Diamond
crystals are generally perfect on all sides. They seldom show
irregular sides or faces by which they were attached to a support,
as do artificial crystals of chemical salts; another proof that the
diamond must have crystallised from a dense liquid.
The accompanying illustration (Fig. 14) shows some of the various
crystalline forms of native diamonds.
[Illustration: FIG. 14. CRYSTALLINE FORMS OF NATIVE DIAMONDS.
To face p. 86.]
No. 1. Diamond in the form of a hexakis-octahedron (the forty-eight
scalenohedron), or a solid figure contained by forty-eight scalene
triangles. According to Professor Maskelyne, this occurs as a
self-existent form only in the diamond.
No. 2. Diamond in the form of a hexakis-octahedron and
octahedron. From Sudafrika.
No. 3. Diamond in the form of octahedron with intersections.
No. 4. Diamond from Brazil.
No. 5. Diamond from Kimberley.
No. 6. Diamond from Brazil.
No, 7. A macle or twin crystal, showing its formation from an
octahedron with curved edges.
* * * * *
Some crystals of diamonds have their surfaces beautifully marked
with equilateral triangles, interlaced and of varying sizes
(Fig. 15). Under the microscope these markings appear as hollow
depressions sharply cut out of the surrounding surface, and
these depressions were supposed by Gustav Rose to indicate the
probability that the diamonds had at some previous time been
exposed to incipient combustion. Rose pointed out that similar
triangular striations appeared on the surfaces of diamonds burnt
before the blowpipe. This experiment I have repeated on a clear
diamond, and I have satisfied myself that during combustion
before the blowpipe, in the field of a microscope, the surface is
etched with triangular markings different in character from those
naturally on crystals (Fig. 16). The artificial striæ are very
irregular, much smaller, and massed closer together, looking as
if the diamond during combustion flaked away in triangular chips,
while the markings natural to crystals appear as if produced by
the crystallising force as they were being built up. Many crystals
of chemical compounds appear striated from both these causes.
Geometrical markings can be produced by eroding the surface of a
crystal of alum with water, and they also occur naturally during
crystallisation.
[Illustration: FIG. 15. TRIANGULAR MARKINGS ON NATURAL FACE OF A
DIAMOND CRYSTAL.]
[Illustration: FIG. 16. TRIANGULAR MARKINGS ARTIFICIALLY PRODUCED
ON A DIAMOND CRYSTAL.
To face page 88.]
CHAPTER VIII
PHYSICAL AND CHEMICAL PROPERTIES OF THE DIAMOND
I need scarcely say the diamond is almost pure carbon, and it is
the hardest substance in nature.
When heated in air or oxygen to a temperature varying from 760°
to 875° C., according to its hardness, the diamond burns with
production of carbonic acid. It leaves an extremely light ash,
sometimes retaining the shape of the crystal, consisting of iron,
lime, magnesia, silica, and titanium. In boart and carbonado
the amount of ash sometimes rises to 4 per cent, but in clear
crystallised diamonds it is seldom higher than 0·05 per cent. By
far the largest constituent of the ash is iron.
The following table shows the temperatures of combustion in oxygen
of different kinds of carbon:
°C.
Condensed vapour of carbon 650
Carbon from sugar, heated in an electrical furnace 660
Artificial graphites, generally 660
Graphite from ordinary cast-iron 670
Carbon from blue ground, of an ochre colour 690
Carbon from blue ground, very hard and black 710
Diamond, soft Brazilian 760
Diamond, hard Kimberley 780
Boart from Brazil 790
Boart from Kimberley 790
Boart, very hard, almost impossible to cut 900
HARDNESS
Diamonds vary considerably in hardness, and even different parts
of the same crystal differ in their resistance to cutting and
grinding.
Beautifully white diamonds have been found at Inverel, New South
Wales, and from the rich yield of the mine and the white colour of
the stones great things were expected. In the first parcel which
came to England the stones were found to be so much harder than
South African diamonds that it was at first feared they would be
useless except for rock-boring purposes. The difficulty of cutting
them disappeared with improved appliances, and they now are highly
prized.
The famous Koh-i-noor, when being cut into its present form, showed
a notable variation in hardness. In cutting one of the facets near
a yellow flaw, the crystal became harder and harder the further
it was cut, until, after working the mill for six hours at the
usual speed of 2400 revolutions a minute, little impression was
made. The speed was increased to more than 3000, when the work
slowly proceeded. Other portions of the stone were found to be
comparatively soft, and became harder as the outside was cut away.
The intense hardness of the diamond can be illustrated by the
following experiment. On the flattened apex of a conical block
of steel place a diamond, and upon it bring down a second cone
of steel. On forcing together the two steel cones by hydraulic
pressure the stone is squeezed into the steel blocks without
injuring it in the slightest degree.
In an experiment I made at Kimberley the pressure gauge showed 60
atmospheres, and the piston being 3·2 inches diameter, the absolute
pressure was 3·16 tons, equivalent on a diamond of 12 square mm.
surface to 170 tons per square inch of diamond.
The use of diamond in glass-cutting I need not dwell on. So hard is
diamond in comparison to glass, that a suitable splinter of diamond
will plane curls off a glass plate as a carpenter’s tool will plane
shavings off a deal board. The illustration (Fig. 17) shows a few
diamond-cut glass shavings.
DENSITY OR SPECIFIC GRAVITY
The specific gravity of the diamond varies ordinarily from 3·514
to 3·518. For comparison, I give in tabular form the specific
gravities of the different varieties of carbon and of the minerals
found on the sorting tables:
SPECIFIC
GRAVITY.
Amorphous carbon 1·45-1·70
Hard gas coke 2·356
Hard graphite 2·5
Quartzite and granite 2·6
Beryl 2·7
Mica 2·8
Hornblende 3·0
Boart 3·47-3·49
Carbonado 3·50
Diamond 3·514-3·518
Garnet 3·7
Corundum 3·8
Zircon 4·4
Barytes 4·5
Chrome and titanic iron ore 4·7
Magnetite 5·0
There is a substance, the double nitrate of silver and thallium,
which, while solid at ordinary temperatures, liquefies at 75° C.
and then has a specific gravity of 4·5. Admixture with water lowers
the density to any desired point.
If a glass cell is taken containing this liquid diluted to a
density of about 3·6, and in it is thrown pieces of the above-named
minerals, all those whose density is lower than 3·6 will rise to
the surface, while the denser minerals will sink. If now a little
water is carefully added with constantly stirring until the density
of the liquid is reduced to that of the diamond, the heterogeneous
collection sorts itself into three parts. The graphite, quartz,
beryl, mica, and hornblende rise to the surface; the garnet,
corundum, zircons, etc., sink to the bottom, while the diamonds
float in the middle of the liquid. With a platinum landing-net I
can skim off the swimmers and put them into one dish; with the
same net I can fish out the diamonds and put them in a second
dish, while by raising a sieve at the bottom I can remove the heavy
minerals and put them into a third. The accurate separation of
diamonds from the heterogeneous mixture can be effected in less
time than is taken to describe the experiment.
The table shows that diamonds vary somewhat in density among
themselves, between narrow limits. Occasionally, however, diamonds
overpass these figures. Here is an illustration. In a test-tube of
the same dense liquid are three selected diamonds. One rises to the
top, another floats uncertain where to settle, rising and falling
as the temperature of the sorting liquid is raised or lowered,
whilst the third sinks to the bottom. Allowing the liquid to cool
a degree or two slightly increases the density and sends all three
to the surface.
PHOSPHORESCENCE OF DIAMOND
After exposure for some time to the sun many diamonds glow in
a dark room. Some diamonds are fluorescent, appearing milky in
sunlight. In a vacuum, exposed to a high-tension current of
electricity, diamonds phosphoresce of different colours, most South
African diamonds shining with a bluish light. Diamonds from other
localities emit bright blue, apricot, pale blue, red, yellowish
green, orange, and pale green light. The most phosphorescent
diamonds are those which are fluorescent in the sun. One beautiful
green diamond in the writer’s collection, when phosphorescing in a
good vacuum, gives almost as much light as a candle, and you can
easily read by its rays. But the time has hardly come when diamonds
can be used as domestic illuminants! The emitted light is pale
green, tending to white, and in its spectrum, when strong, can be
seen bright lines, one at about λ 5370 in the green, one at λ 5130
in the greenish blue, and one at λ 5030 in the blue. A beautiful
collection of diamond crystals belonging to Professor Maskelyne
phosphoresces with nearly all the colours of the rainbow, the
different faces glowing with different shades of colour. Diamonds
which phosphoresce red generally show the yellow sodium line on
a continuous spectrum. In one Brazilian diamond phosphorescing a
reddish-yellow colour I detected in its spectrum the citron line
characteristic of yttrium.
The rays which make the diamond phosphoresce are high in the
ultra-violet. To illustrate this phosphorescence under the
influence of the ultra-violet rays, arrange a powerful source
of these rays, and in front expose a design made up of certain
minerals, willemite, franklinite, calcite, etc.--phosphorescing
of different colours. Their brilliant glow ceases entirely when a
thin piece of glass is interposed between them and the ultra-violet
lamp.
I now draw attention to a strange property of the diamond, which
at first sight might seem to discount the great permanence and
unalterability of this stone. It has been ascertained that the
cause of phosphorescence is in some way connected with the
hammering of the electrons, violently driven from the negative
pole on to the surface of the body under examination, and so great
is the energy of the bombardment, that impinging on a piece of
platinum or even iridium, the metal will actually melt. When the
diamond is thus bombarded in a radiant matter tube the result is
startling. It not only phosphoresces, but becomes discoloured,
and in course of time becomes black on the surface. Some diamonds
blacken in the course of a few minutes, while others require an
hour or more to discolour. This blackening is only superficial,
and although no ordinary means of cleaning will remove the
discolouration, it goes at once when the stone is polished with
diamond powder. Ordinary oxidising reagents have little or no
effect in restoring the colour.
[Illustration: FIG. 17. DIAMOND-CUT GLASS AND SHAVINGS.]
[Illustration: FIG. 18. DIAMONDS IN RÖNTGEN RAYS.
A. BLACK DIAMOND IN GOLD FRAME.
B. PINK DELHI DIAMOND.
C. PASTE IMITATION OF B.
To face p. 98.]
The superficial dark coating on a diamond after exposure to
molecular bombardment I have proved to be graphite. M. Moissan has
shown that this graphite, on account of its great resistance to
oxidising reagents, cannot have been formed at a lower temperature
than 3600° C.
It is thus manifest that the bombarding electrons, striking the
diamond with enormous velocity, raise the superficial layer to the
temperature of the electric arc and turn it into graphite, whilst
the mass of diamond and its conductivity to heat are sufficient to
keep down the general temperature to such a point that the tube
appears scarcely more than warm to the touch.
A similar action occurs with silver, the superficial layers of
which can be raised to a red heat without the whole mass becoming
more than warm.
CONVERSION OF DIAMOND INTO GRAPHITE
Although we cannot convert graphite into diamond, we can change
the diamond into graphite. A clear crystal of diamond is placed
between two carbon poles, and the poles with intervening diamond
are brought together and an arc formed between. The temperature of
the diamond rapidly rises, and when it approaches 3600° C., the
vaporising point of carbon, it breaks down, swells, and changes
into black and valueless graphite.
TRIBO-LUMINESCENCE
A few minerals give out light when rubbed. In the year 1663 the
Hon. Robert Boyle read a paper before the Royal Society, in which
he described several experiments made with a diamond which markedly
showed tribo-luminescence. As specimens of tribo-luminescent bodies
I may instance sphalerite (sulphide of zinc), and an artificial
sphalerite, which is even more responsive to friction than the
native sulphide.[6]
Mrs. Kunz, wife of the well-known New York mineralogist, possesses,
perhaps, the most remarkable of all phosphorescing diamonds. This
prodigy diamond will phosphoresce in the dark for some minutes
after being exposed to a small pocket electric light, and if rubbed
on a piece of cloth a long streak of phosphorescence appears.
ABSORPTION SPECTRUM OF DIAMOND
On passing a ray of light through a diamond and examining it in a
spectroscope, Walter has found in all colourless brilliants of over
1 carat in weight an absorption band at wave-length 4155 (violet).
He ascribes this band to an impurity and suggests it may possibly
be due to samarium. Three other fainter lines were detected in the
ultra-violet by means of photography.
REFRACTIVITY
But it is not the hardness of the diamond so much as its optical
qualities that make it so highly prized. It is one of the most
refracting substances in nature, and it also has the highest
reflecting properties. In the cutting of diamonds advantage is
taken of these qualities. When cut as a brilliant the facets on
the lower side are inclined so that light falls on them at an
angle of 24° 13´, at which angle all the incident light is totally
reflected. A well-cut brilliant should appear opaque by transmitted
light except at a small spot in the middle where the table and
culet are opposite. All the light falling on the front of the
stone is reflected from the facets, and the light passing into the
diamond is reflected from the interior surfaces and refracted
into colours when it passes out into the air, giving rise to the
lightnings, the effulgence, and coruscations for which the diamond
is supreme above all other gems.
The following table gives the refractive indices of diamonds and
other bodies:
REFRACTIVE INDICES FOR THE D LINE
Chromate of lead 2·50-2·97
Diamond 2·47-2·75
Phosphorus 2·22
Sulphur 2·12
Ruby 1·78
Thallium glass 1·75
Iceland spar 1·65
Topaz 1·61
Beryl 1·60
Emerald 1·59
Flint glass 1·58
Quartz 1·55
Canada balsam 1·53
Crown glass 1·53
Fluor-spar 1·44
Ice 1·31
In vain I have searched for a liquid of the same refraction as
diamond. Such a liquid would be invaluable to the merchant, as
on immersing a stone the clear body would absolutely disappear,
leaving in all their ugliness the flaws and black specks so
frequently seen even in the best stones.
THE DIAMOND AND POLARISED LIGHT
Having no double refraction, the diamond should not act on
polarised light. But as is well known, if a transparent body which
does not so act is submitted to strain of an irregular character
it becomes doubly refracting, and in the polariscope reveals the
existence of the strain by brilliant colours arranged in a more or
less defined pattern, according to the state of tension in which
the crystal exists. I have examined many hundred diamond crystals
under polarised light, and with few exceptions the colours show how
great is the strain to which some of them are exposed. On rotating
the polariser, the black cross most frequently seen revolves round
a particular point in the inside of the crystal; on examining
this point with a high power we sometimes see a slight flaw, more
rarely a minute cavity. The cavity is filled with gas at enormous
pressure, and the strain is set up in the stone by the effort of
the gas to escape. I have already said that the great Cullinan
diamond by this means revealed a state of considerable internal
stress and strain.
So great is this strain of internal tension that it is not uncommon
for a diamond to explode soon after it reaches the surface, and
some have been known to burst in the pockets of the miners or when
held in the warm hand. Large crystals are more liable to burst than
smaller pieces. Valuable stones have been destroyed in this way,
and it is whispered that cunning dealers are not averse to allowing
responsible clients to handle or carry in their warm pockets large
crystals fresh from the mine. By way of safeguard against explosion
some dealers imbed large diamonds in raw potato to ensure safe
transit to England.
The anomalous action which many diamonds exert on polarised light
is not such as can be induced by heat, but it can easily be
conferred on diamonds by pressure, showing that the strain has not
been produced by sudden cooling, but by sudden lowering of pressure.
The illustration of this peculiarity is not only difficult, but
sometimes exceedingly costly--difficult because it is necessary to
arrange for projecting on the screen the image of a diamond crystal
between the jaws of a hydraulic press, the illuminating light
having to pass through delicate optical polarising apparatus--and
costly because only perfectly clear crystals can be used, and
crystals of this character sometimes fly to pieces as the pressure
rises. At first no colour is seen on the screen, the crystal not
being birefringent. A movement of the handle of the press, however,
gives the crystal a pinch, instantly responded to by the colours on
the screen, showing the production of double refraction. Another
movement of the handle brightens the colours, and a third may
strain the crystal beyond its power of resistance, when the crystal
flies to pieces.
THE DIAMOND AND RÖNTGEN RAYS
The diamond is remarkable in another respect. It is extremely
transparent to the Röntgen rays, whereas highly refracting glass,
used in imitation diamonds, is almost perfectly opaque to the rays.
I exposed for a few seconds over a photographic plate to the X-rays
the large Delhi diamond of a rose-pink colour weighing 31½ carats,
a black diamond weighing 23 carats, and a glass imitation of the
pink diamond (Fig. 18). On development the impression where the
diamond obscured the rays was found to be strong, showing that
most rays passed through, while the glass was practically opaque.
By this means imitation diamonds can readily be distinguished from
true gems.
ACTION OF RADIUM ON DIAMOND
The β-rays from radium having like properties to the stream of
negative electrons in a radiant matter tube, it was of interest to
ascertain if they would exert a like difference on diamond. The
diamond glows under the influence of the β-radiations, and crushed
diamond cemented to a piece of card or metal makes an excellent
screen in a spinthariscope--almost as good as zinc sulphide. Some
colourless crystals of diamond were imbedded in radium bromide and
kept undisturbed for more than twelve months. At the end of that
time they were examined. The radium had caused them to assume a
bluish-green colour, and their value as “fancy stones” had been
increased.
This colour is persistent and penetrates below the surface. It
is unaffected by long-continued heating in strong nitric acid and
potassium chlorate, and is not discharged by heating to redness.
To find out if this prolonged contact with radium had communicated
to the diamond any radio-active properties, six diamonds were put
on a photographic plate and kept in the dark for a few hours. All
showed radio-activity by darkening the sensitive plate, some being
more-active than others. Like the green tint, the radio-activity
persists after drastic treatment. To me this proves that
radio-activity does not merely consist in the adhesion of electrons
or emanations given off by radium to the surface of an adjacent
body, but the property is one involving layers below the surface,
and like the alteration of tint, is probably closely connected with
the intense molecular excitement the stone had experienced during
its twelve months’ burial in radium bromide.
A diamond that had been coloured by radium, and had acquired
strong radio-active properties, was slowly heated to dull redness
in a dark room. Just before visibility a faint phosphorescence
spread over the stone. On cooling and examining the diamond it was
found that neither the colour nor the radio-activity had suffered
appreciably.
BOILING- AND MELTING-POINT OF CARBON
On the average the critical point of a substance is 1·5 times its
absolute boiling-point. Therefore the critical point of carbon
should be about 5800° Ab. But the absolute critical temperature
divided by the critical pressure is for all the elements so far
examined never less than 2·5; this being about the value Sir James
Dewar finds for hydrogen. So that, accepting this, we get the
maximum critical pressure as follows, viz. 2320 atmospheres:
(5800° Ab.)/CrP = 2.5, or CrP = (5800 Ab.)/2.5,
or 2320 atmospheres.
Carbon and arsenic are the only two elements that have a
melting-point above the boiling-point; and among compounds carbonic
acid and fluoride of silicium are the only other bodies with
similar properties. Now the melting-point of arsenic is about
1·2 times its absolute boiling-point. With carbonic acid and
fluoride of silicium the melting-points are about 1·1 times their
boiling-points. Applying these ratios to carbon, we find that its
melting-point would be about 4400°.
Therefore, assuming the following data:
Boiling-point 3870° Ab.
Melting-point 4400°
Critical temperature 5800°
Critical pressure 2320 Ats.
the Rankine or Van der Waals formula, calculated from the
boiling-point and critical data, would be as follows:
log. P = 10·11 - 39120/T,
and this gives for a temperature of 4400° Ab. a pressure of 16·6
Ats. as the melting-point pressure. The results of the formula are
given in the form of a table:
Temperature Pressure
Ab. Ats.
3870° 1·00 Boiling-point.
4000° 2·14
4200° 6·25
4400° 16·6 Melting-point.
4600° 40·4
4800° 91·2
5000° 193
5200° 386
5400° 735
5600° 1330
5800° 2320 Critical point (15 tons per square inch).
[Illustration: FIG. 19. CURVE OF VAPOUR PRESSURE OF CARBON]
If, then, we may reason from these rough estimates, above a
temperature of 5800° Ab. no amount of pressure will cause carbon
vapour to assume liquid form, whilst at 4400° Ab. a pressure
of above 17 atmospheres would suffice to liquefy some of it.
Between these extremes the curve of vapour pressure is assumed to
be logarithmic, as represented in the accompanying diagram. The
constant 39120 which occurs in the logarithmic formula enables
us to calculate the latent heat of evaporation. If we assume the
vapour density to be normal, or the molecule in vapour as C_{2},
then the heat of volatilisation of 12 grms. of carbon would
be 90,000 calories; or, if the vapour is a condensed molecule
like C_{6}, then the 12 grms. would need 30,000 calories. In the
latter case the evaporation of 1 grm. of carbon would require
2500 calories, whereas a substance like zinc needs only about 400
calories.
CHAPTER IX
GENESIS OF THE DIAMOND
Speculations as to the probable origin of the diamond have been
greatly forwarded by patient research, and particularly by improved
means of obtaining high temperatures, an advance we owe principally
to the researches of the late Professor Moissan.
Until recent years carbon was considered absolutely non-volatile
and infusible; but the enormous temperatures placed at the disposal
of experimentalists by the introduction of electricity show
that, instead of breaking rules, carbon obeys the same laws that
govern other bodies. It volatilises at the ordinary pressure at a
temperature of about 3600° C., and passes from the solid to the
gaseous state without liquefying. It has been found that other
bodies, such as arsenic, which volatilise without liquefying at
the ordinary pressure, will easily liquefy if pressure is added to
temperature. It naturally follows that if along with the requisite
temperature sufficient pressure is applied, liquefaction of carbon
will take place, when on cooling it will crystallise. But carbon at
high temperatures is a most energetic chemical agent, and if it can
get hold of oxygen from the atmosphere or any compound containing
it, it will oxidise and fly off in the form of carbonic acid. Heat
and pressure therefore are of no avail unless the carbon can be
kept inert.
It has long been known that iron, when melted, dissolves carbon,
and on cooling liberates it in the form of graphite. Moissan
discovered that several other metals, especially silver, have
similar properties; but iron is the best solvent for carbon. The
quantity of carbon entering into solution increases with the
temperature.
[Illustration: FIG. 20. MOISSAN’S ELECTRIC FURNACE.
To face p. 116.]
For the artificial manufacture of diamond the first necessity is
to select pure iron--free from sulphur, silicon, phosphorus,
etc.--and to pack it in a carbon crucible with pure charcoal from
sugar. The crucible is then put into the body of the electric
furnace and a powerful arc formed close above it between carbon
poles, utilising a current of 700 ampères at 40 volts pressure
(Fig. 20). The iron rapidly melts and saturates itself with carbon.
After a few minutes’ heating to a temperature above 4000° C.--a
temperature at which the iron melts like wax and volatilises in
clouds--the current is stopped and the dazzling fiery crucible is
plunged beneath the surface of cold water, where it is held till
it sinks below a red heat. As is well known, iron increases in
volume at the moment of passing from the liquid to the solid state.
The sudden cooling solidifies the outer layer of iron and holds
the inner molten mass in a tight grip. The expansion of the inner
liquid on solidifying produces an enormous pressure, and under the
stress of this pressure the dissolved carbon separates out in
transparent forms--minutely microscopic, it is true--all the same
veritable diamonds, with crystalline form and appearance, colour,
hardness, and action on light, the same as the natural gem.
Now commences the tedious part of the process. The metallic ingot
is attacked with hot nitro-hydrochloric acid until no more iron
is dissolved. The bulky residue consists chiefly of graphite,
together with translucent chestnut-coloured flakes of carbon,
black opaque carbon of a density of from 3·0 to 3·5 and hard as
diamonds--black diamonds or carbonado, in fact--and a small portion
of transparent, colourless diamonds showing crystalline structure.
Besides these there may be carbide of silicon and corundum, arising
from impurities in the materials employed.
The residue is first heated for some hours with strong sulphuric
acid at the boiling-point, with the cautious addition of powdered
nitre. It is then well washed and for two days allowed to soak in
strong hydrofluoric acid in cold, then in boiling acid. After this
treatment the soft graphite disappears, and most, if not all, the
silicon compounds have been destroyed. Hot sulphuric acid is again
applied to destroy the fluorides, and the residue, well washed, is
attacked with a mixture of the strongest nitric acid and powdered
potassium chlorate, kept warm--but not above 60° C., to avoid
explosions. This treatment must be repeated six or eight times,
when all the hard graphite will gradually be dissolved and little
else left but graphitic oxide, diamond, and the harder carbonado
and boart. The residue is fused for an hour in fluorhydrate or
fluoride of potassium, then boiled out in water and again heated
in sulphuric acid. The well-washed grains which resist this
energetic treatment are dried, carefully deposited on a slide, and
examined under the microscope. Along with numerous pieces of black
diamond are seen transparent, colourless pieces, some amorphous,
others with a crystalline appearance. Fig. 21 B shows one of these
crystalline fragments. Although many fragments of crystals occur,
it is remarkable I have never seen a complete crystal. All appear
shattered, as if on being liberated from the intense pressure
under which they were formed they burst asunder. I have singular
evidence of this phenomenon. A fine piece of artificial diamond,
carefully mounted by me on a microscopic slide, exploded during
the night and covered the slide with fragments. Moissan’s crystals
of artificial diamond sometimes broke a few weeks after their
preparation, and some of the diamonds which cracked weeks or even
months after their preparation showed fissures covered with minute
cubes. I have explained that this bursting paroxysm is not unknown
at the Kimberley mines. So far, all such artificial diamonds are
microscopic. The largest artificial diamond is less than one
millimetre across.
[Illustration: FIG. 21. ARTIFICIAL DIAMOND MADE BY THE AUTHOR FROM
MOLTEN IRON.]
[Illustration: FIG. 22. MOISSAN’S ARTIFICIAL DIAMONDS.
To face p. 120.]
These laboratory diamonds burn in the air before the blowpipe to
carbonic acid. In lustre, crystalline form, optical properties,
density, and hardness they are identical with the natural stone.
In several cases Moissan separated ten to fifteen microscopic
diamonds from a single ingot. The larger of these are about 0·75
mm. long, the octahedra being 0·2 mm.
The accompanying illustrations (Fig. 22) are copied from drawings
in Moissan’s book _Le Four Electrique_.
Along with carbon, molten iron dissolves other bodies which possess
tinctorial powers. We know of blue, green, pink, yellow, and orange
diamonds. One batch of iron might contain an impurity colouring the
stones blue, another lot would tend towards the formation of pink
stones, another of green, and so on. Cobalt, nickel, chromium, and
manganese, all metals present in the blue ground, would produce
these colours.
A NEW FORMATION OF DIAMOND
I have long speculated as to the possibility of obtaining
artificially such pressures and temperatures as would fulfil the
above conditions. In their researches on the gases from fired
gunpowder and cordite, Sir Frederick Abel and Sir Andrew Noble
obtained in closed steel cylinders pressures as great as 95 tons
to the square inch, and temperatures as high as 4000° C. According
to a paper recently communicated to the Royal Society, Sir Andrew
Noble, exploding cordite in closed vessels, has obtained a pressure
of 8000 atmospheres, or 50 tons per square inch, with a temperature
reaching in all probability 5400° Ab.
Here, then, we have conditions favourable for the liquefaction of
carbon, and were the time of explosion sufficient to allow the
reactions to take place, we should certainly expect to get the
liquid carbon to solidify in the crystalline state.[7]
By the kindness of Sir Andrew Noble I have been enabled to work
upon some of the residues obtained in closed vessels after
explosions, and I have submitted them to the same treatment that
the granulated iron had gone through. After weeks of patient toil
I removed the amorphous carbon, the graphite, the silica,[8] and
other constituents of the ash of cordite, and obtained a residue
among which, under the microscope, crystalline particles could be
distinguished. Some of these particles, from their crystalline
appearance and double refraction, were silicon carbide; others
were probably diamonds. The whole residue was dried and fused at a
good red heat in an excess of potassium bifluoride, to which was
added, during fusion, 5 per cent of nitre. (Previous experiments
had shown me that this mixture readily attacked and dissolved
silicon carbide; unfortunately it also attacks diamond to a slight
degree.) All the operations of washing and acid treatment were
performed in a large platinum crucible by decantation (except the
preliminary attack with nitric acid and potassium chlorate, when a
hard glass vessel was used); the final result was washed into a
shallow watch-glass and the selection made under the microscope.
The residue, after thorough washing and then heating in fuming
sulphuric acid, was washed, and the largest crystalline particles
picked out and mounted.
From the treatment the residual crystals had undergone, chemists
will agree with me that diamonds only could stand such an ordeal;
on submitting them to skilled crystallographic authorities my
opinion is confirmed. Speaking of the largest crystal, one eminent
authority calls it “a diamond showing octahedral planes with
dark boundaries due to high refracting index.” After careful
examination, another authority writes of the same crystal diamond,
“I think one may safely say that the position and angles of its
faces, and of its cleavages, the absence of birefringence, and the
high refractive index are all compatible with the properties of the
diamond crystallising in the form of an octahedron. Others of the
remaining crystals, which show a similar high refractive index,
appeared to me to present the same features.”
It would have been more conclusive had I been able to get further
evidence as to the density and hardness of the crystals; but from
what I have already said I think there is no doubt that in these
closed vessel explosions we have another method of producing the
diamond artificially.
CHAPTER X
THE NATURAL FORMATION OF THE DIAMOND
An hypothesis is of little value if it only elucidates half a
problem. Let us see how far we can follow out the ferric hypothesis
to explain the volcanic pipes. In the first place we must remember
these so-called volcanic vents are admittedly not filled with the
eruptive rocks, scoriaceous fragments, etc., constituting the
ordinary contents of volcanic ducts.
Certain artificial diamonds present the appearance of an elongated
drop. I have seen diamonds which have exactly the appearance of
drops of liquid separated in a pasty condition and crystallised
on cooling. Diamonds are sometimes found with little appearance
of crystallisation, but with rounded forms similar to those
which a liquid might assume if kept in the midst of another
liquid with which it would not mix. Other drops of liquid carbon
retained for sufficient time above their melting-point would
coalesce with adjacent drops, and on slow cooling would separate
in the form of large perfect crystals. Two drops, joining after
incipient crystallisation, might assume the not uncommon form of
interpenetrating twin crystals.
Many circumstances point to the conclusion that the diamond of
the chemist and the diamond of the mine are strangely akin as to
origin. It is evident that the diamond has not been formed _in
situ_ in the blue ground. The genesis must have taken place at vast
depths under enormous pressure. The explosion of large diamonds
on coming to the surface shows extreme tension. More diamonds are
found in fragments and splinters than in perfect crystals; and it
is noteworthy that although these splinters and fragments must be
derived from the breaking up of a large crystal, yet in only one
instance have pieces been found which could be fitted together, and
these occurred at different levels. Does not this fact point to the
conclusion that the blue ground is not their true matrix? Nature
does not make fragments of crystals. As the edges of the crystals
are still sharp and unabraded, the _locus_ of formation cannot have
been very distant from the present sites. There were probably many
sites of crystallisation differing in place and time, or we should
not see such distinctive characters in the gems from different
mines, nor indeed in the diamonds from different parts of the same
mine.
I start with the reasonable supposition that at a sufficient
depth[9] there were masses of molten iron at great pressure and
high temperature, holding carbon in solution, ready to crystallise
out on cooling. Far back in time the cooling from above caused
cracks in superjacent strata through which water[10] found its way.
On reaching the incandescent iron the water would be converted
into gas, and this gas would rapidly disintegrate and erode the
channels through which it passed, grooving a passage more and more
vertical in the necessity to find the quickest vent to the surface.
But steam in the presence of molten or even red-hot iron liberates
large volumes of hydrogen gas, together with less quantities of
hydrocarbons[11] of all kinds--liquid, gaseous, and solid. Erosion
commenced by steam would be continued by the other gases; it would
be easy for pipes, large as any found in South Africa, to be
scored out in this manner.
Sir Andrew Noble has shown that when the screw stopper of his
steel cylinders in which gunpowder explodes under pressure is not
absolutely perfect, gas escapes with a rush so overpowering and a
temperature so high as to score a wide channel in the metal. To
illustrate my argument Sir Andrew Noble has been kind enough to try
a special experiment. Through a cylinder of granite he drilled a
hole 0·2 inch diameter, the size of a small vent. This was made the
stopper of an explosion chamber, in which a quantity of cordite was
fired, the gases escaping through the granite vent. The pressure
was about 1500 atmospheres and the whole time of escape was less
than half a second. The erosion produced by the escaping gases and
by the heat of friction scored out a channel more than half an
inch diameter and melted the granite along the course. If steel
and granite are thus vulnerable at comparatively moderate gaseous
pressure, it is easy to imagine the destructive upburst of hydrogen
and water-gas, grooving for itself a channel in the diabase and
quartzite, tearing fragments from resisting rocks, covering the
country with debris, and finally, at the subsidence of the great
rush, filling the self-made pipe with a water-borne magma in which
rocks, minerals, iron oxide, shale, petroleum, and diamonds are
violently churned in a veritable witch’s cauldron! As the heat
abated the water vapour would gradually give place to hot water,
which, forced through the magma, would change some of the mineral
fragments into the existing forms of to-day.
Each outbreak would form a dome-shaped hill; the eroding agency of
water and ice would plane these eminences until all traces of the
original pipes were lost.
Actions such as I have described need not have taken place
simultaneously. As there must have been many molten masses
of iron with variable contents of carbon, different kinds of
colouring matter, solidifying with varying degrees of rapidity,
and coming in contact with water at intervals throughout long
periods of geological time--so must there have been many outbursts
and upheavals, giving rise to pipes containing diamonds. And
these diamonds, by sparseness of distribution, crystalline
character, difference of tint, purity of colour, varying hardness,
brittleness, and state of tension, have the story of their origin
impressed upon them, engraved by natural forces--a story which
future generations of scientific men may be able to interpret with
greater precision than is possible to-day.
CHAPTER XI
METEORIC DIAMONDS
Sensational as is the story of the diamond industry in South
Africa, quite another aspect fixes the attention of the chemist.
The diamonds come out of the mines, but how did they get in? How
were they formed? What is their origin?
Gardner Williams, who knows more about diamonds than any man
living, is little inclined to indulge in speculation. In his
fascinating book he frankly says:
“I have been frequently asked, ‘What is your theory of the original
crystallisation of the diamond?’ and the answer has always been, ‘I
have none; for after seventeen years of thoughtful study, coupled
with practical research, I find that it is easier to “drive a coach
and four” through most theories that have been propounded than to
suggest one which would be based on any non-assailable data.’
All that can be said is that in some unknown manner carbon, which
existed deep down in the internal regions of the earth, was changed
from its black and uninviting appearance to the most beautiful gem
which ever saw the light of day.”
Another diamond theory appeals to the imagination. It is said
the diamond is a gift from Heaven, conveyed to earth in meteoric
showers. The suggestion, I believe, was first broached by A.
Meydenbauer,[12] who says, “The diamond can only be of cosmic
origin, having fallen as a meteorite at later periods of the
earth’s formation. The available localities of the diamond contain
the residues of not very compact meteoric masses which may,
perhaps, have fallen in prehistoric ages, and which have penetrated
more or less deeply, according to the more or less resistant
character of the surface where they fell. Their remains are
crumbling away on exposure to the air and sun, and the rain has
long ago washed away all prominent masses. The enclosed diamonds
have remained scattered in the river beds, while the fine light
matrix has been swept away.”
According to this hypothesis, the so-called volcanic pipes are
simply holes bored in the solid earth by the impact of monstrous
meteors--the larger masses boring the holes, while the smaller
masses, disintegrating in their fall, distributed diamonds
broadcast. Bizarre as such a theory appears, I am bound to say
there are many circumstances which show that the notion of the
heavens raining diamonds is not impossible.
The most striking confirmation of the meteoric theory comes from
Arizona. Here, on a broad open plain, over an area about five
miles in diameter, have been scattered one or two thousand masses
of metallic iron, the fragments varying in weight from half a ton
to a fraction of an ounce. There is no doubt these masses formed
part of a meteoric shower, although no record exists as to when
the fall took place. Curiously enough, near the centre, where most
of the meteorites have been found, is a crater with raised edges
three-quarters of a mile in diameter and about 600 feet deep,
bearing exactly the appearance which would be produced had a mighty
mass of iron struck the ground and buried itself deep under the
surface. Altogether, ten tons of this iron have been collected, and
specimens of the Canyon Diablo meteorite are in most collectors’
cabinets.
An ardent mineralogist--the late Dr. Foote--cutting a section of
this meteorite, found the tools were injured by something vastly
harder than metallic iron. He examined the specimen chemically,
and soon after announced to the scientific world that the Canyon
Diablo meteorite contained black and transparent diamonds. This
startling discovery was afterwards verified by Professors Moissan
and Friedel, and Moissan, working on 183 kilogrammes of the Canyon
Diablo meteorite, has recently found smooth black diamonds and
transparent diamonds in the form of octahedra with rounded edges,
together with green, hexagonal crystals of carbon silicide. The
presence of carbon silicide in the meteorite shows that it must at
some time have experienced the temperature of the electric furnace.
Since this revelation the search for diamonds in meteorites has
occupied the attention of chemists all over the world.
Fig. 23 A, C, and D, are reproductions of photographs of true
diamonds I myself have extracted from the Canyon Diablo meteorite.
[Illustration: FIG. 23. DIAMONDS FROM CANYON DIABLO METEORITE.
To face p. 138.]
Under atmospheric influences the iron would rapidly oxidise and
rust away, colouring the adjacent soil with red oxide of iron.
The meteoric diamonds would be unaffected and left on the surface
of the soil, to be found haphazard when oxidation had removed the
last proof of their celestial origin. That there are still lumps of
iron left at Arizona is merely due to the extreme dryness of the
climate and the comparatively short time that the iron has been on
our planet. We are here witnesses to the course of an event which
may have happened in geologic times anywhere on the earth’s surface.
Although in Arizona diamonds have fallen from the skies,
confounding our senses, this descent of precious stones is what may
be called a freak of nature rather than a normal occurrence. To
the modern student of science there is no great difference between
the composition of our earth and that of extra-terrestrial masses.
The mineral peridot is a constant extra-terrestrial visitor,
present in most meteorites. And yet no one doubts that peridot
is also a true constituent of rocks formed on this earth. The
spectroscope reveals that the elementary composition of the stars
and the earth are pretty much the same; and the spectroscope also
shows that meteorites have as much of earth as of heaven in their
composition. Indeed, not only are the selfsame elements present in
meteorites, but they are combined in the same way to form the same
minerals as in the crust of the earth.
It is certain from observations I have made, corroborated
by experience gained in the laboratory, that iron at a high
temperature and under great pressure--conditions existent at great
depths below the surface of the earth--acts as the long-sought
solvent for carbon, and will allow it to crystallise out in the
form of diamond. But it is also certain, from the evidence afforded
by the Arizona and other meteorites, that similar conditions have
existed among bodies in space, and that on more than one occasion a
meteorite freighted with jewels has fallen as a star from the sky.
INDEX
Able, Sir F., closed vessel experiments, 122
Absorption spectrum of diamond, 101
Aliwal North, 6
Alluvial deposits of diamonds, 9
Amygdaloidal trap, 10
Arizona meteor, 136
Arkansas, diamonds in, 2
Ash of diamond, 82, 89
Augite, 20
Automatic diamond collector, 56
Barytes, 71
-- density of, 93
Basalt, 15
Basutos, 12, 39
Bechuanas, 12, 39
Beryl, density of, 93
-- refractive index of, 103
Biotite, 20
Blackening of diamonds, 98
Blue ground, 10, 47
-- -- diamantiferous, 18, 19
Boart, 81,
-- combustion temperature of, 90
-- density of, 93
Boiling-point of carbon, 110
Bonney, Rev. Professor, 67
Boyle on the diamond, 100
Brazil, diamonds in, 4
Breakwater, Cape Town, 36
Breccia, diamantiferous, 19
Brilliant cut diamond, 102
British Association in South Africa, 7
British Guiana, diamonds in, 4
Bronzite, 20, 71
-- hydrated, 19
Bultfontein Mine, 14
-- -- characteristics of diamond from, 64
Bursting of diamonds, 105
Calcite, 20, 97
California, diamonds in, 3
Canada balsam, refractive index of, 103
Canyon Diablo meteorite, 136
Cape Colony, 5
Cape Town, 5
Carat, equivalent in grains, 69
Carbon, boiling and melting point of, 110
-- combustion temperature of, 90
-- critical point of, 110
-- density of, 93
-- dissolved in iron, 116
-- volatilisation of, 115
Carbonado, 81
-- density of, 93
Characteristics of diamonds from the different mines, 64
Chemical properties of diamond, 89
Chromate of lead, refractive index of, 103
Chrome diopside, 71
-- iron, 20
-- -- ore, 71
-- -- -- density of, 93
Chromite, 20
Classification of rough diamonds, 73
Cleavage of diamonds, 78
Coke, density of, 93
Colesberg Kopje, 26
Collecting the gems, 55
Coloured diamonds, 62, 82
Combustion of diamond, 89
-- temperatures of diamond, boart, graphite, and carbon, 90
“Comet” crushers, 49
Compound system, 36, 37
Concentrating and washing machinery, 49
Convict labourers, 71
Cordite, diamond from explosion of, 123
Corundum, 20
-- density of, 93
Cradock, 6
Craters or pipes, 18
Crown glass, refractive index of, 103
Crusher, “Comet,” 49
Crystallisation of diamond, 86
Crystals, octahedra, of diamond, 63, 86
Cullinan diamond, 15, 76, 80, 104
Dallas, Captain, 40
De Beers Consolidated Mines, 7, 33
-- -- floors at Kenilworth, 47
-- -- Mine, 14, 24, 34
-- -- -- characteristics of diamonds from, 64
-- -- strong-room, 74
Delhi diamond, 107
Density of diamond, 57, 93
-- of graphite, 83, 93
-- of stones accompanying diamond, 70, 71, 93, 95
Depositing floors, 46
Dewar, Sir J., conversion of diamond into graphite, 123
Diabase, olivine, 16
Diallage, 20
Diamond, absorption spectrum of, 101
-- and polarised light, 104
-- a new formation of, 122
-- ash of, 82, 89
-- collector, automatic, 56
-- combustion of, 89
-- -- temperature of, 90
-- converted into graphite, 100
-- density of, 57, 93
-- etched by burning, 88
-- explosion of, 120
-- genesis of the, 115
-- in meteors, 134
-- in Röntgen rays, 107
-- matrix of, 67
-- natural formation of, 127
-- Office at Kimberley, 73
-- physical and chemical properties of, 89
-- pipes or craters, 18
-- radio-activity of, 109
-- refractive index of, 103
-- Trade Act, 36
-- triangular markings on, 87
-- tribo-luminescence of, 100
Diamonds, coloured or fancy, 62, 82
-- Maskelyne on, 1
-- noteworthy, 76
-- phosphorescence of, 96
-- produced, weight, value of, 35
-- yield of, from De Beers, 60
Drift, diamonds from the, 12
Duke of Tuscany diamond, 80
Dutch boart, or zircon, 59
Dutoitspan Mine, 14, 23
-- -- characteristics of diamonds from, 64
Eclogite, 20
-- containing diamonds, 67
Electrons, bombardment by, 98
Emerald, refractive index of, 103
Empress Eugenie diamond, 80
Enstatite, 20
Explosion of diamonds, 120
Excelsior diamond, 80
Fancy stones, 62
Fingoes, 39
Flint glass, refractive index of, 103
“Floating Reef,” 21
Floors, depositing, 46
Fluor-spar, refractive index of, 103
Formation, new, of diamond, 122
Fort Beaufort, 6
Franklinite, 97
Frank Smith Mine, 15
-- -- -- characteristics of diamonds from, 66
Fraserburg, 6
Garnet, 20, 70
-- density of, 93
Genesis of the diamond, 115
“Golden fancies,” 65
Granite, 18
-- density of, 93
Graphite, 81, 83
-- combustion temperature of, 90
-- conversion of diamond into, 100
-- density of, 93
-- diamonds coated with, 99
Graphitic oxide, 83, 93
Grease, collecting diamonds by aid of, 57
Hard blue ground, 47
Hardness of diamond, 90
Haulage system, 46
Hexakis-octahedron crystal, 86
Hope blue diamond, the, 80
Hornblende, 71
-- density of, 93
Iceland spar, refractive index of, 103
Ice, refractive index of, 103
I.D.B. laws (Illicit Diamond Buying), 36
Ilmenite, 20
India, diamonds in, 4
Inverel diamonds, 91
Internal strain in diamonds, 104
Iron a solvent for carbon, 116
-- ore, density of, 93
-- pyrites, 20
Jagersfontein diamond, 79
-- Mine, 14
-- -- characteristics of diamonds from, 68
Jeffreysite, 20
Kafirs, 42
Kamfersdam Mine, 15
-- -- characteristics of diamonds from, 66
Kenilworth depositing floors, 47
Kimberley, 6
-- blue ground, 10
-- mines, 14, 23, 34
-- Mine in old days, 25
-- -- at the present day, 34
-- -- characteristics of diamonds from, 63
-- shales, 15
-- West Mine, 15
-- -- -- characteristics of diamonds from, 66
Kirsten’s automatic diamond collector, 57
Klipdam, 8, 23
Koffyfontein Mine, 14
Koh-i-noor diamond, 80
-- hardness of, 91
Kyanite, 20, 71
Lamp, ultra-violet, 97
Leicester Mine, 15, 23
-- -- characteristics of diamonds from, 67
Loterie d’Angleterre diamond, 80
Lustre of rough diamonds, 56
Machinery for washing and concentrating, 49
Macles, 86
Magnetite, 20, 71
-- density of, 93
Maskelyne on diamonds, 1
Matabele, 12, 39
Matrix of diamond, 67
Melaphyre, 10, 16
Melting-point of carbon, 110
Meteor, Canyon Diablo, 136
Meteoric diamonds, 134
Meydenbauer on meteoric diamonds, 135
Mica, 20, 71
-- density of, 93
Moissan’s experiments on the genesis of diamond, 115
Mud volcano, 24
Nassak diamond, 80
Natal, coal in, 6
Natural formation of diamond, 127
Newlands Mine, 15
-- -- characteristics of diamonds from, 67
New Rush diggings, 26
Nizam of Hyderabad diamond, 80
Noble, Sir A., experiments, 122, 131
Noteworthy diamonds, 76
Octahedral crystals of diamond, 63, 86
Olivine, 20
-- diabase, 16
Orange River Colony, coal in, 6
-- -- -- diamonds in, 14
Orloff diamond, 80
Pasha of Egypt diamond, 80
Paterson, Mr., description of Kimberley in old days, 25
Peridot, 20, 139
Peridotite, 3
Perofskite, 20
Phosphorescence of diamonds, 96
Phosphorus, refractive index of, 103
Physical properties of diamond, 89
Picking tables, 51
Pipes or craters, 18
Pitt diamond, 80
Polarised light and diamond, 104
Pole Star diamond, 80
Pondos, 39, 42
Premier Mine, 15, 76
Prodigious diamonds, 76
Pseudobrookite, 20
Pulsator, 52
Pyrope, 70
Quartzite, 16, 20
-- density of, 93
-- refractive index of, 103
Radio-activity of diamond, 109
Radium, action on diamond, 108
“Reef,” 21
Refractive indices, 103
Refractivity of diamond, 102
Regent diamond, 80
Reunert, Mr., description of Kimberley Mine, 30
Rhodes, Cecil John, 34
River washings, 7
Rock shafts, 43
Röntgen rays, diamond in, 107
Ruby, refractive index of, 103
Rutile, 20
Sahlite, 20
Sancy diamond, 80
Savings of the native workmen, 41
Scalenohedron diamond crystal, 86
Serpentine, 19
Shafts, rock, 43
Shah diamond, 80
Shales, Kimberley, 15
Shangains, 39
Shells in blue ground, 21
Shot boart, 81
Silver and thallium, nitrate of, 94
Smaragdite, 20
Soft blue ground, 47
Sorting the diamantiferous gravel, 55
Specific gravity, _see_ Density
Spectrum, absorption of diamond, 101
Sphalerite, 100
Spinthariscope, 108
Sprat’s _History of the Royal Society_, 1
Sprouting graphite, 84
Star of the South diamond, 80
Stones other than diamonds, 70, 71, 93, 95
Strain, internal, in diamonds, 104
Sulphur, refractive index of, 103
Swazis, 39
Ultra-violet lamp to show phosphorescence, 97
Underground workings, 43
United States, diamonds in, 2
Vaalite, 20
Vaal River, 8, 16
Valuators, 73
Value of diamonds per carat, 12, 69
Value of diamonds, progressive increase in, 69
Vermiculite, 20
Volatilisation of carbon, 115
Volcanic necks, 18
Volcano, mud, 24
Wages, scale of, 35
Washing and concentrating machinery, 49
Wesselton Mine, 14, 15, 23, 35
-- -- characteristics of diamonds from, 65
Willemite, 97
Wollastonite, 20
Workings, underground, 43
Yellow ground, diamantiferous, 19
Yield of diamonds, annual, 60
-- -- -- total, 35
-- falls off with depth, 68
-- per load of blue ground, 62
Zimbabwe ruins, 40
Zircon, 20, 59, 71
-- density of, 93
Zulus, 12, 39, 40
W. BRENDON AND SON, LTD., PRINTERS, PLYMOUTH
FOOTNOTES:
[1] _Chemical News_, Vol. I, p. 208.
[2] Mr. Paterson called “limey stuff” what is now termed “blue
ground.” It was also formerly called “marl stuff,” “blue stuff,”
and “blue clay.”
[3] The original name for the Kimberley Mine. It was also sometimes
known as “Colesberg Kopje.”
[4] _Diamonds and Gold in South Africa._ By T. Reunert.
Johannesburg, 1893.
[5] According to Gardner Williams the South African carat is
equivalent to 3·174 grains. In Latimer Clark’s _Dictionary of
Metric and other Useful Measures_ the diamond carat is given as
equal to 3·1683 grains = 0·2053 gramme = 4 diamond grains; 1
diamond grain = 0·792 troy grain; 151·5 diamond carats = 1 ounce
troy.
Webster’s _International Dictionary_ gives the diamond carat as
equal to 3⅕ troy grains.
_The Oxford English Dictionary_ says the carat was originally 1/144
of an ounce, or 3⅓ grains, but now equal to about 3⅕ grains, though
varying slightly with time and place.
The _Century Dictionary_ says the diamond carat is equal to about
3⅙ troy grains, and adds that in 1877 the weight of the carat was
fixed by a syndicate of London, Paris, and Amsterdam jewellers at
205 milligrammes. This would make the carat equal to 3·163 troy
grains. A law has been passed in France ordaining that in the
purchase or sale of diamonds and other precious stones the term
“metric carat” shall be employed to designate a weight of 200
milligrammes (3·086 grains troy), and prohibiting the use of the
word carat to designate any other weight.
[6] Artificial tribo-luminescent sphalerite:--
Zinc carbonate 100 parts
Flower of sulphur 30 ”
Manganese sulphate ½ per cent.
Mix with distilled water and dry at a gentle heat. Put in luted
crucible and keep at a bright red heat for from two to three hours.
[7] Sir James Dewar, in a Friday evening discourse at the Royal
Institution in 1880, showed an experiment proving that the
temperature of the interior of a carbon tube heated by an outside
electric arc was higher than that of the oxy-hydrogen flame. He
placed a few small crystals of diamond in the carbon tube, and,
maintaining a current of hydrogen to prevent oxidation, raised the
temperature of the tube in an electric furnace to that of the arc.
In a few minutes the diamond was transformed into graphite. At
first sight this would seem to show that diamond cannot be formed
at temperatures above that of the arc. It is probable, however, for
reasons given above, that at exceedingly high pressures the result
would be different.
[8] The silica was in the form of spheres, perfectly shaped and
transparent, mostly colourless, but among them several of a ruby
colour. When 5 per cent of silica was added to cordite, the residue
of the closed vessel explosion contained a much larger quantity of
these spheres.
[9] A pressure of fifteen tons on the square inch would exist not
many miles beneath the surface of the earth.
[10] There are abundant signs that a considerable portion of this
part of Africa was once under water, and a fresh-water shell has
been found in apparently undisturbed blue ground at Kimberley.
[11] The water sunk in wells close to the Kimberley mine is
sometimes impregnated with paraffin, and Sir H. Roscoe extracted a
solid hydrocarbon from the “blue ground.”
[12] _Chemical News_, vol. lxi, p. 209, 1890.
TRANSCRIBER’S NOTE
Obvious typographical errors and punctuation errors have been
corrected after careful comparison with other occurrences within
the text and consultation of external sources.
All misspellings in the text, and inconsistent or archaic usage,
have been retained: for example, unfrequent; clayey; friable;
slaty; imbed; stoped; peculation; situate.
In the Table of Contents, the Index page number ‘145’ has been
replaced by ‘141’.
In the Index, ‘Colesberg Copje’ has been replaced by
‘Colesberg Kopje’, and ‘DeBeers’ has been replaced by
‘De Beers’.
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