OCCURRENCE OF DIAMOND
The whole of the diamonds known in ancient times were obtained from
the so-called Golconda mines in India. Golconda itself, now a deserted
fortress near Hyderabad, was merely the mart where the diamonds were
bought and sold. The diamond-bearing district actually spread over a
wide area on the eastern side of the Deccan, extending from the Pinner
River in the Madras Presidency northwards to the Rivers Son and Khan,
tributaries of the Ganges, in Bundelkhand. The richest mines, where
the large historical stones were found, are in the south, mostly
near the Kistna River. The diamonds were discovered in sandstone,
or conglomerate, or the sands and gravels of river-beds. The mines
were visited in the middle of the seventeenth century by the French
traveller and jeweller, Tavernier, when travelling on a commission
for Louis XIV, and he afterwards published a careful description of
them and of the method of working them. The mines seem to have been
exhausted in the seventeenth century; at any rate, the prospecting,
which has been spasmodically carried on during the last two centuries,
has proved almost abortive. With the exception of the Koh-i-nor, all
the large Indian diamonds were probably discovered not long before
Tavernier’s visit. The diamonds known to Pliny, and in his time, were
quite small, and it is doubtful if any stones of considerable size came
to light before A.D. 1000.
India enjoyed the monopoly of supplying the world’s demand for diamonds
up to the discovery, in 1725, of the precious stone in Brazil. Small
stones were detected by the miners in the gold washings at Tejuco,
about eighty miles (129 km.) from Rio de Janeiro, in the Serro do Frio
district of the State of Minas Geraes. The discovery naturally caused
great excitement. So many diamonds were found that in 1727 something
like a slump took place in their value. In order to keep up prices, the
Dutch merchants, who mainly controlled the Indian output, asserted that
the diamonds had not been found in Brazil at all, but were inferior
Indian stones shipped to Brazil from Goa. The tables were neatly turned
when diamonds were actually shipped from Brazil to Goa, and exported
thence to Europe as Indian stones. This course and the continuous
development of the diamond district in Brazil rendered it impossible
to hoodwink the world indefinitely. The drop in prices was, however,
stayed by the action of the Portuguese government, who exacted such
heavy duties and imposed such onerous conditions that finally no one
would undertake to work the mines. Accordingly, in 1772 diamond-mining
was declared a royal monopoly in Brazil, and such it remained until
the severance of Brazil from Portugal in 1834, when private mining was
permitted by the new government subject to the payment of reasonable
royalties. The industry was enormously stimulated by the discovery, in
1844, of the remarkably rich fields in the State of Bahia, especially
at Serra da Cincorá, where carbonado, or black diamond, first came to
light, but after a few years, owing to the difficulties of supplying
labour, the unhealthiness of the climate, and the high cost of living,
the yield fell off and gradually declined, until the importance of the
fields was finally eclipsed by the rise of the South African mines.
The Brazilian mines have proved very productive, but chiefly in small
diamonds, stones above a carat in weight being few in comparison. The
largest stone, to which the name, the Star of the South, was applied,
weighed in the rough 254½ carats; it was discovered at the Bagagem
mines in 1853. The quality of the diamonds is good, many of them having
the highly-prized bluish-white colour. The principal diamond-bearing
districts of Brazil centre at Diamantina, as Tejuco was re-named
after the discovery of diamonds, Grão Magor, and Bagagem in the State
of Minas Geraes, at Diamantina in the State of Bahia, and at Goyãz
and Matto Grosso in the States of the same names. The diamonds occur
chiefly in _cascalho_, a gravel, containing large masses of quartz
and small particles of gold, which is supposed to be derived from a
quartzose variety of micaceous slate known as itacolumite. The mines
are now to some extent being worked by systematic dredging of the
river-beds.
Early in 1867 the children of a Boer farmer, Daniel Jacobs, who dwelt
near Hopetown on the banks of the Orange River, picked up in the course
of play near the river a white pebble, which was destined not only to
mark the commencement of a new epoch in the record of diamond mines,
but to change the whole course of the history of South Africa. This
pebble attracted the attention of a neighbour, Schalk van Niekerk, who
suspected that it might be of some value, and offered to buy it. Mrs.
Jacobs, however, gave it him, laughingly scouting the idea of accepting
money for a mere pebble. Van Niekerk showed it to a travelling trader,
by name John O’Reilly, who undertook to obtain what he could for it on
condition that they shared the proceeds. Every one he met laughed to
scorn the idea that the stone had any value, and it was once thrown
away and only recovered after some search in a yard, but at length he
showed it to Lorenzo Boyes, the Acting Civil Commissioner at Colesberg,
who, from its extreme hardness, thought it might be diamond and sent
it to the mineralogist, W. Guybon Atherston, of Grahamstown, for
determination. So uncertain was Boyes of its value that he did not even
seal up the envelope containing it, much less register the package.
Atherston found immediately that the long-scorned pebble was really
a fine diamond, weighing 21-3/16 carats, and with O’Reilly’s consent
he submitted it to Sir Philip Wodehouse, Governor at the Cape. The
latter purchased it at once for £500, and dispatched it to be shown
at the Paris Exhibition of that year. It did not, however, attract
much attention; chimerical tales of diamond finds in remote parts of
the world are not unknown. Indeed, for some time only a few small
stones were picked up beside the Orange River, and no one believed in
the existence of any extensive diamond deposit. However, all doubt as
to the advisibility of prospecting the district was settled by the
discovery of the superb diamond, afterwards known as the ‘Star of
South Africa,’ which was picked up in March 1869 by a shepherd boy
on the Zendfontein farm near the Orange River. Van Niekerk, on the
alert for news of further discoveries, at once hurried to the spot and
purchased the stone from the boy for five hundred sheep, ten oxen, and
a horse, which seemed to the boy untold wealth, but was not a tithe of
the £11,200 which Lilienfeld Bros., of Hopetown, gave Van Niekerk.
[Illustration: _PLATE XV_
KIMBERLEY MINE, 1871]
[Illustration: _PLATE XVI_
KIMBERLEY MINE, 1872]
This remarkable discovery attracted immediate attention to the
potentialities of a country which produced diamonds of such a size, and
prospectors began to swarm into the district, gradually spreading up
the Vaal River. For some little time not much success was experienced,
but at length, early in 1870, a rich find was made at Klipdrift,
now known as Barkly West, which was on the banks of the Vaal River
immediately opposite the Mission camp at Pniel. The number of miners
steadily increased until the population on the two sides of the river
included altogether some four or five thousand people, and there was
every appearance of stability in the existing order of things. But a
vast change came over the scene upon the discovery of still richer
mines lying to the south-east and some distance from the river. The
ground was actually situated on the route traversed by parties hurrying
to the Vaal River, but no one dreamed of the wealth that lay under
their feet. The first discovery was made in August 1870 at the farm
Jagersfontein, near Fauresmith in Orange River Colony, by De Klerk,
the intelligent overseer, who noticed in the dry bed of a stream a
number of garnets, and, knowing that they often accompanied diamond,
had the curiosity to investigate the point. He was immediately
rewarded by finding a fine diamond weighing 50 carats. In the following
month diamonds were discovered about twenty miles from Klipdrift
at Dutoitspan on the Dorstfontein farm, and a little later also on
the contiguous farm of Bultfontein; a diamond was actually found in
the mortar used in the homestead of the latter farm. Early in May
1871 diamonds were found about two miles away on De Beers’ farm,
Vooruitzigt, and two months later, in July, a far richer find was made
on the same farm at a spot which was first named Colesberg Kopje, the
initial band of prospectors having come from the town of that name
near the Orange River, but was subsequently known as Kimberley after
the Secretary of State for the Colonies at that time. Soon a large
and prosperous town sprang up close to the mines; it rapidly grew
in size and importance, and to this day remains the centre of the
diamond-mining industry. Subsequent prospecting proved almost blank
until the discovery of the Premier or Wesselton mine on Wesselton
farm, about four miles from Kimberley, in September 1890; it received
the former name after Rhodes, who was Premier of Cape Colony at that
date. No further discovery of any importance was made until, in 1902,
diamonds were found about twenty miles north-west-north of Pretoria in
the Transvaal, at the new Premier mine, now famed as the producer of
the gigantic Cullinan diamond.
[Illustration: _PLATE XVII_
KIMBERLEY MINE, 1874]
[Illustration: _PLATE XVIII_
KIMBERLEY MINE, 1881]
The Kimberley mines were at first known as the ‘dry diggings’ on
account of their arid surroundings in contradistinction to the ‘river
diggings’ by the Vaal. The dearth of water was at first one of the
great difficulties in the way of working the former mines, although
subsequently the accumulation of underground water at lower levels
proved a great obstacle to the working of the mines. The ‘river
diggings’ were of a type similar to that met with in India and Brazil,
the diamonds occurring in a gravelly deposit of limited thickness
beneath which was barren rock, but the Kimberley mines presented a
phenomenon hitherto without precedent in the whole history of diamond
mining. The diamonds were found in a loose surface deposit, which was
easily worked, and for some time the prospectors thought that the
underlying limestone corresponded to the bedrock of the river gravel,
until at length one more curious than his fellows investigated the
yellowish ground underneath, and found to his surprise that it was even
richer than the surface layer. Immediately a rush was made back to the
deserted claims, and the mines were busier than ever. This ‘yellow
ground,’ as it is popularly called, was much decomposed and easy,
therefore, to work and sift. About fifty to sixty feet (15-18 m.) below
the surface, however, it passed into a far harder rock, which from its
colour is known as the ‘blue ground’; this also, to the unexpected
pleasure of the miners, turned out to contain diamonds. Difficulties
arose as each claim, 30 by 30 Dutch feet (about 31 English feet or
9·45 metres square) in area, was worked downwards. In the Kimberley
mine (Plate XVI) access to the various claims was secured by retaining
parallel strips, 15 feet wide, each claim being, therefore, reduced
in width to 22½ feet, to form roadways running from side to side of
the mine in one direction. These, however, soon gave way, not only
because of the falling of the earth composing them, but because they
were undermined and undercut by the owners of the adjacent claims.
By the end of 1872 the last roadway had disappeared, and the mine
presented the appearance of a vast pit. In order to obtain access to
the claims without intruding on those lying between, and to provide for
the hauling of the loads of earth to the surface, an ingenious system
of wire cables in three tiers (Plate XVII) was erected, the lowest
tier being connected to the outermost claims, the second to claims
farther from the edge, and the highest to claims in the centre of the
pit. The mine at that date presented a most remarkable spectacle,
resembling an enormous radiating cobweb, which had a weird charm by
night as the moonlight softly illuminated it, and by day, owing to
the perpetual ring of the flanged wheels of the trucks on the running
wires, twanged like some gigantic æolian harp. This system fulfilled
its purpose admirably until, with increasing depth of the workings,
other serious difficulties arose. Deprived of the support of the hard
blue ground, the walls of the mine tended to collapse, and additional
trouble was caused by the underground water that percolated into the
mine. By the end of 1883 the floor of the Kimberley mine was almost
entirely covered by falls of ‘reef’ (Plate XVIII), as the surrounding
rocks are termed, the depth then being about 400 feet (122 m.). In the
De Beers mine, in spite of the precaution taken to prevent falls of
reef by cutting the walls of the mine back in terraces, falls occurred
continuously in 1884, and by 1887, at a depth of 350 feet (107 m.),
all attempts at open working had to be abandoned. In the Dutoitspan
mine buttresses of blue ground were left, which held back the reef for
some years, but ultimately the mine became unsafe, and in March 1886 a
disastrous fall took place, in which eighteen miners—eight white men
and ten Kafirs—lost their lives. The Bultfontein mine was worked to the
great depth of 500 feet (152 m.), but falls occurred in 1889 and put
an end to open working. In all cases, therefore, the ultimate end was
the same: the floor of the mine became covered with a mass of worthless
reef, which rendered mining from above ground dangerous, and, indeed,
impossible except at prohibitive cost. It was then clearly necessary
to effect access to the diamond-bearing ground by means of shafts sunk
at a sufficient distance from the mine to remove any fear of falls of
reef. For such schemes co-operative working was absolutely essential.
Plate XIX illustrates the desolate character of the Kimberley mine
above ground and the vastness of the yawning pit, which is over 1000
feet (300 m.) in depth.
[Illustration: _PLATE XIX_
KIMBERLEY MINE AT THE PRESENT DAY]
[Illustration: _PLATE XX_
WESSELTON (_open_) MINE]
A certain amount of linking up of claims had already taken place, but,
although many men must have seen that the complete amalgamation of the
interests in each mine was imperative, two men alone had the capacity
to bring their ideas to fruition. C. J. Rhodes was the principal agent
in the formation in April 1880 of the De Beers Mining Company, which
rapidly absorbed the remaining claims in the mine, and was re-formed
in 1887 as the De Beers Consolidated Mining Company. Meantime, Barnett
Isaacs, better known by the cognomen Barnato, which had been adopted by
his
brother Henry when engaged in earning his livelihood in the diamond
fields as an entertainer, had secured the major interests in the
Kimberley mine. Rhodes saw that, for effective working of the two
mines by any system of underground working, they must be under one
management, but to all suggestions of amalgamation Barnato remained
deaf, and at last Rhodes determined to secure control of the Kimberley
mine at all costs. The story of the titanic struggle between these
two men forms one of the epics of finance. Eventually, when shares
in the Kimberley mine had been boomed to an extraordinary height,
and the price of diamonds had fallen as low as 18s. a carat, Barnato
gave way, and in July 1889 the Kimberley mine was absorbed by the De
Beers Company on payment of the enormous sum of £5,338,650. Shortly
afterwards they undertook the working of the Dutoitspan and the
Bultfontein mines, and in January 1896 they acquired the Premier or
Wesselton mine. The interests in the Jagersfontein mine were in 1888
united in the New Jagersfontein Mining and Exploration Company, and
the mine is now worked also by the De Beers Company. Thus, until the
development of the new Premier mine in the Transvaal, the De Beers
Company practically controlled the diamond market. The development
of this last mine was begun so recently, and its size is so vast—the
longest diameter being half a mile—that open-cut working is likely to
continue for some years.
[Illustration: _PLATE XXI_
LOADING THE BLUE GROUND ON THE FLOORS, AND PLOUGHING IT OVER]
[Illustration: _PLATE XXII_
WASHING-MACHINES FOR CONCENTRATING THE BLUE GROUND]
Though varying slightly in details, the methods of working the mines
are identical in principle. From the steeply inclined shaft horizontal
galleries are run diagonally right across the mine, the vertical
interval between successive galleries being 40 feet. From each
gallery side galleries are run at right angles to it and parallel to
the working face. The blue ground is worked systematically backwards
from the working face. The mass is stoped, _i.e._ drilled and broken
from the bottom upwards, until only a thin roof is left. As soon as the
section is worked out and the material removed, the roof is allowed
to fall in, and work is begun on the next section of the same level;
at the same time the first section on the level next below is opened
out. Thus work is simultaneously carried on in several levels, and a
vertical plane would intersect the working faces in a straight line
obliquely inclined to the vertical direction (Fig. 60). When freshly
mined, the blue ground is hard and compact, but it soon disintegrates
under atmospheric influence. Indeed, the yellow ground itself was
merely decomposed blue ground. No immediate attempt is made, therefore,
to retrieve the precious stones. The blue ground is spread on to
the ‘floors’ (Plate XXI), _i.e._ spaces of open veldt which have
been cleared of bushes and inequalities, to the depth of a couple of
feet, and remains there for periods ranging from six months to two
years, depending on the quality of the blue ground and the amount of
rainfall. To hasten the disintegration the blue ground is frequently
ploughed over and occasionally watered, a remarkable introduction of
agricultural methods into mining operations. No elaborate patrolling
or guarding is required, because the diamonds are so sparsely, though
regularly, scattered through the mass that even of the actual workers
in the mines but few have ever seen a stone in the blue ground. When
sufficiently broken up, it is carted to the washing and concentrating
machines, by means of which the diamonds and the heavier constituents
are separated from the lighter material.
[Illustration: FIG. 60.—Vertical Section of Diamond Pipe, showing
Tunnels and Stopes.]
Formerly the diamonds were picked out from the concentrates by means
of the keen eyes of skilled natives; but the process has been vastly
simplified and the risk of theft entirely eliminated by the remarkable
discovery made in 1897 by F. Kirsten, of the De Beers Company, that
of all the heavy constituents of the blue ground diamond alone, with
the exception of an occasional corundum and zircon, which are easily
sorted out afterwards, adheres to grease more readily than to water.
In this ingenious machine, the ‘jigger’ or ‘greaser’ (Plate XXIII) as
it is commonly termed, the concentrates are washed over a series of
galvanized-iron trays, which are covered with a thick coat of grease.
The trays are slightly inclined downwards, and are kept by machinery
in constant sideways motion backwards and forwards. So accurate is the
working of this device that few diamonds succeed in getting beyond
the first tray, and none progress as far as the third, which is added
as an additional precaution. The whole apparatus is securely covered
in so that there is no risk of theft during the operation. The trays
are periodically removed, and the grease is scraped off and boiled to
release the diamonds, the grease itself being used over again on the
trays. This is the first time in the whole course of extraction from
the mines that the diamonds are actually handled. The stones are now
passed on to the sorters, who separate them into parcels according to
their size, shape, and quality.
[Illustration: _PLATE XXIII_
DIAMOND-SORTING MACHINES]
[Illustration: _PLATE XXIV_
KAFIRS PICKING OUT DIAMONDS]
The classification at the mines is first into groups by the shape:
(1) close goods, (2) spotted stones, (3) rejection cleavage, (4)
fine cleavage, (5) light brown cleavage, (6) ordinary and rejection
cleavage, (7) flats, (8) macles, (9) rubbish, (10) boart. Close goods
are whole crystals which contain no flaws and can be cut into single
stones. Spotted stones, as their name suggests, contain spots which
necessitate removal, and cleavage includes stones which are so full of
flaws that they have to be cleaved or split into two or more stones.
Flats are distorted octahedra, and macles are twinned octahedra.
Rubbish is material which can be utilized only for grinding purposes,
and boart consists of round dark stones which are invaluable for
rock-drills. These groups are afterwards graded into the following
subdivisions, depending on increasing depth of yellowish tint: (_a_)
blue-white, (_b_) first Cape, (_c_) second Cape, (_d_) first bye, (_e_)
second bye, (_f_) off-colour, (_g_) light yellow, (_h_) yellow. It is,
however, only the first group that is so minutely subdivided. After
being purchased, the parcels are split up again somewhat differently
for the London market (cf. p. 136), and the dealers re-arrange the
stones according to the purpose for which they are required. Formerly
a syndicate of London merchants took the whole of the produce of the
Kimberley mines at a previously arranged price per carat, but at
the present time the diamonds are sold by certain London firms on
commission.
The products of each mine show differences in either form or colour
which enable an expert readily to recognize their origin. The old
diggings by the Vaal River yielded finer and more colourless stones
than those found in the dry diggings and the mines underlying them. The
South African diamonds, taken as a whole, are always slightly yellowish
or ‘off-coloured’; the mines are, indeed, remarkable for the number of
fine and large, canary-yellow and brown, stones produced. The Kimberley
mine yields a fair percentage of white, and a large number of twinned
and yellow stones. The yield of the De Beers mine comprises mostly
tinted stones—yellow and brown, occasionally silver capes, and very
seldom stones free from colour. The Dutoitspan mine is noted for its
harvest of large yellow diamonds; it also produces fine white cleavage
and small white octahedra. The stones found in the Bultfontein mine are
small and spotted, but, on the other hand, the yield has been unusually
regular. The Premier or Wesselton mine yields a large proportion
of flawless octahedra, but, above all, a large number of beautiful
deep-orange diamonds. Of all the South African mines the Jagersfontein
in the Orange River Colony alone supplies stones of the highly-prized
blue-white colour and steely lustre characteristic of the old Indian
stones. The new Premier mine in the Transvaal is prolific, but mostly
in off-coloured and low-grade stones, the Cullinan diamond being a
remarkable exception.
To illustrate the amazing productiveness of the South African mines,
it may be mentioned that, according to Gardner F. Williams, the
Kimberley group of mines in sixteen years yielded 36 million carats
of diamonds, and the annual output of the Jagersfontein mine averages
about a quarter of a million carats, whereas the total output of the
Brazil mines, for the whole of the long period during which they have
been worked, barely exceeds 13 million carats. The average yield of the
South African mines, however, perceptibly diminishes as the depth of
the mines increases.
The most interesting point connected with the South African diamond
mines, viewed from the scientific standpoint, is the light that they
have thrown on the question of the origin of the diamond, which
previously was an incomprehensible and apparently insoluble problem.
In the older mines, just as at the river diggings by the Vaal, the
stones are found in a gravelly deposit that has resulted from the
disintegration of the rocks through which the adjacent river has
passed, and it is clear that the diamond cannot have been formed _in
situ_ here; it had been suspected, and now there is no doubt, that the
itacolumite rock of Brazil has consolidated round the diamonds which
are scattered through it, and that it cannot be the parent rock. The
occurrence at Kimberley is very different. These mines are funnels
which go downwards to unknown depths; they are more or less oval in
section, becoming narrower with increasing depth, and are evidently the
result of some eruptive agency. The Kimberley mine has been worked to
a depth of nearly 4000 feet (1200 m.), and no signs of a termination
have as yet appeared. The blue ground which fills these ‘pipes,’ as
they are termed, must have been forced up from below, since it is
sharply differentiated from the surrounding country rocks. This blue
ground is a brecciated peridotite of peculiar constitution, to which
the well-known petrologist, Carvil Lewis, who made a careful study
of it, gave the name kimberlite. The blue colour testifies to its
richness in iron, and it is to the oxidation of the iron constituent,
that the change of colour to yellow in the upper levels is due. Owing
to the shafts that have been sunk for working the mines, the nature
of the surrounding rocks is known to some depth. Immediately below
the surface is a decomposed ferriferous basalt, about 20 to 90 feet
(6-27 m.) thick, next a black slaty shale, 200 to 250 feet (60-75 m.)
thick, then 10 feet (3 m.) of conglomerate, next 400 feet (120 m.)
of olivine diabase, then quartzite, about 400 feet (120 m.) thick,
and lastly a quartz porphyry, which has not yet been penetrated. The
strata run nearly horizontal, and there are no signs of upward bending
at the pipes. The whole of the country, including the mines, was
covered with a red sandy soil, and there was nothing to indicate the
wealth that lay underneath. The action of water had in process of time
removed all signs of eruptive activity. The principal minerals which
are associated with diamond in the blue ground are magnetite, ilmenite,
chromic pyrope, which is put on the market as a gem under the misnomer
‘Cape-ruby,’ ferriferous enstatite, which also is sometimes cut,
olivine more or less decomposed, zircon, kyanite, and mica.
The evidence produced by an examination of the blue ground and the
walls of the pipes proves that the pipes cannot have been volcanoes
such as Vesuvius. There is no indication whatever of the action of any
excessive temperature, while, on the other hand, there is every sign of
the operation of enormous pressure; the diamonds often contain liquid
drops of carbonic acid. Crookes puts forward the plausible theory that
steam has been the primary agency in propelling the diamond and its
associates up into the channel through which it has carved its way to
freedom, and holds that molten iron has been the solvent for carbon
which has crystallized out as diamond under the enormous pressures
obtaining in remote depths of the earth’s crust. It is pertinent to
note that, by dissolving carbon in molten iron, the eminent chemist,
Moissan, was enabled to manufacture tiny diamond crystals. Water
trickling down from above would be immediately converted into steam at
very high pressure on coming into contact with the molten iron, and, in
its efforts to escape, the steam would drive the iron and its precious
contents, together with the adjacent rocks, upwards to the surface. The
ferriferous nature of the blue ground and the yellow tinge so common
to the diamonds lend confirmation to this theory. The process by which
the carbon was extracted from shales or other carboniferous rocks and
dissolved in iron still awaits elucidation.
Diamonds were found in New South Wales as long ago as 1851 on Turon
River and at Reedy Creek, near Bathurst, about ninety miles (145 km.)
from Sydney, but the find was of little commercial importance. A more
extensive deposit came to light in 1867 farther north at Mudgee. In
1872 diamonds were discovered in the extreme north of the State, at
Bingara near the Queensland border. Another discovery was made in 1884
at Tingha, and still more recently in the tin gravels of Inverell in
the same region. In their freedom from colour and absence of twinning
the New South Wales diamonds resemble the Brazilian stones. The average
size is small, running about five to the carat when cut; the largest
found weighed nearly 6 carats when cut. They are remarkable for their
excessive hardness; they can be cut only with their own dust, ordinary
diamond dust making no impression.
The Borneo diamonds are likewise distinguished by their exceptional
hardness. They mostly occur by the river Landak, near Pontianak on the
west coast of the island. They are found in a layer of rather coarse
gravel, variable, but rarely exceeding a yard (1 m.), in depth, and are
associated with corundum and rutile, together with the precious metals
gold and platinum. Indeed, it is no uncommon sight to see natives
wearing waistcoats ornamented with gold buttons, in each of which a
diamond is set. The diamonds are well crystallized and generally of
pure water; yellowish and canary-yellow stones are also common, but
rose-red, bluish, smoky, and black stones are rare. They seldom exceed
a carat in weight; but stones of 10 carats in weight are found, and
occasionally they attain to 20 carats. In 1850 a diamond weighing 77
carats was discovered. The Rajah of Mattan is said to possess one of
the purest water weighing as much as 367 carats, but no one qualified
to pronounce an opinion regarding its genuineness has ever seen it.
In Rhodesia small diamonds have been found in gravel beds resting on
decomposed granite near the Somabula forest, about 12 miles (19 km.)
west of Gwelo, in association with chrysoberyl in abundance, blue
topaz, kyanite, ruby, sapphire, tourmaline, and garnet.
The occurrence of diamond in German South-West Africa is very peculiar.
Large numbers of small stones are found close to the shore near
Luderitz Bay in a gravelly surface layer, which is nowhere more than a
foot in depth. They are picked by hand by natives and washed in sieves.
In shape they are generally six-faced octahedra or twinned octahedra,
simple octahedra being rare, and in size they run about four or five
to the carat, the largest stone as yet found being only 2 carats in
weight. Their colour is usually yellowish.
Several isolated finds of diamonds have been reported in California
and other parts of the United States, but none have proved of any
importance. The largest stone found weighed 23¾ carats uncut; it was
discovered at Manchester in Virginia.