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Diamond.--The diamond is the hardest substance known. It is, however, very brittle. Chemically it is pure carbon; it is combustible, infusible, and unassailable by acids. In the rough form it is devoid of brilliancy and is only semi-transparent. It is usually cut in one of the three forms, termed the brilliant, rose, and table, the first being the best for developing all its beauty. The double-cut brilliant was formerly square with a high crown, but with the advent of the South African stones and the American cutter the brilliants were cut round with a rather flat crown. Recently in America a modification of the rose brilliant forms of cutting with twenty facets, has been patented under the name of 20th century cutting. Besides their use in jewellery and glass - cutting, diamonds have numerous industrial applications. They are used for jewelling watches, 100 or 200 of them, when prepared for this purpose, weighing only one carat (34 grains or 205 milligrammes). Diamond powder is used for drilling and polishing. Mounted diamond points are used for engraving, and the black variety is used for the cutting of millstones, and in the crown of rotatory rock drills. Recent researches have shown that the rays emitted by radio-active bodies induce fluorescence in diamonds. In this way, diamonds can be distinguished from other precious stones. Years ago, the fluorescence of diamonds under the influence of various coloured rays was noted, and Chaumet has ascertained that there is a close relationship between this fluorescent pro

perty and the brilliancy of diamonds under artificial light, particularly candle light, which brings out most clearly the quality of first-class stones. The most sparkling stones show a notable fluorescence of a very luminous and clear blue. In a jewel-case in which are grouped diamonds of all qualities, the gems when illuminated by violet light, assume different tints from a vivid blue to sombre violet. As soon as the light removed all derees of phosphorescence are noticeable, the jewel-case appearing to be studded with glow-worms, some very bright, others almost extinct; the most sparkling stone will be found to be the best.

The origin of the diamond has long been a matter of discussion. It seems probable that diamonds have been formed by crystallisation from molten rock masses. Minute crystals of diamond have been found with graphite in slowly-cooled steel, and in meteorites. Mr. E. F. Heneage has arrived at the conclusion that the diamonds of South Africa were formed at a very great depth in the various pipes from accumulations of carbonic acid. The difficulty of reproducing these conditions of great heat and pressure artificially has been overcome by Professor Moissan, who found that iron, at a high temperature and under great pressure, will act as a solvent for carbon, and will allow it to crystallise out in the form of diamond. The diamond is usually found as loose crystals in alluvial deposits, The most important of these deposits are those of India and Brazil. The former deposits were known in very early times, and Golconda was the centre of the diamond trade of the antique world. At the present time the diamond production of India is insignificant. The Brazilian diamonds were discovered in 1728. The provinces of Minas Geraes and Bahia are the most productive. The diamonds are found in alluvial deposits derived from the materials brought down from the hills bordering the higher parts of the valleys. It is estimated that since the opening of the Brazilian mines they have yielded altogether three tons of diamonds. The output in 1902 was 40,000 carats. In Borneo diamonds are found with gold. The production in 1901 was 1,972 carats. Since the introduction of the South African supplies the production has fallen. The famous Borneo diamond, of 367 carats, known as the 'Matan," from the territorial title of the Rajah to whom it belongs, has been thought to be the largest known, and was estimated to be worth £269,378. The

Dutch made very large offers of money and warlike material for it early in the 19th century, but they were always refused. The stone, it appears, was examined in 1868, and proved to be only a rock crystal with a specific gravity of 263, thus confirming doubts previously expressed as to its being really a diamond. About 95 per cent. of the world's supply of diamonds is produced in South Africa. The diamond mines of the Kimberley field have been described in papers read before the Society by Professor J. Tennant* in 1870, and by Mr. R. W. Murray+ in 1880; and in 1893 I read a paper describing a visit to the mines. Since then many changes have have taken place, and a brief account of the development of the industry may not be out of place. The story of the accidental discovery of the diamond fields in 1867 has often been told. The first diggings were river washings, for the existence of diamonds away from the Vaal was not suspected, until, in 1870, garnets were discovered on a Boer farm, and diamonds were looked for. This caused the great rush to Kimberley. The mines were worked as deep, open quarries, the diggers working independently, and a system of aerial ropeways was developed, that made the mines look like a spider's web. In 1879, continued falls of rock from the sides of the excavations, and the constant influx of water, led to the idea of sinking shafts at the side of the quarry, and of reaching the diamond ground by underground galleries. As time went on, excessive competition reduced the price of diamonds to the lowest ebb, and Cecil Rhodes and others associated with him conceived the idea of amalgamating the various companies. The amalgamation was skilfully accomplished, and the De Beers Consolidated Mines, Ltd., acquired control of the diamond trade of the world, the cheque finally paid in 1889 for the shares in the Kimberley Central Company being. the largest drawn up to that date. The five mines at Kimberley, the De Beers, Kimberley, Du Toitspan, Bultfontein, and Wesselton, occur in a circle four and a-half miles in diameter. The deposits are evidently the result of the filling-in of extinct craters with volcanic mud from below. The matrix of the diamond, the blue ground, is a breccia composed of shale, basalt, and diorite cemented together by olivine rock. The weathered upper portion of the blue ground is known as yellow ground; and this is what was worked in the early days,

• Journal of the Society of Arts, vol. 19, p. 15. +Ibid, vol. 29, p. 370.

# [bid, vol. 41, p. 168,

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the blue ground being then thought to be bedrock. In 1887, Mr. Gardner F. Williams introduced a system of mining in which all the tlue ground is removed by overhand stoping from the rock wall farthest from the shaft, the broken surrounding rock being allowed to run in and fill up the stopes. The levels are 40 feet apart, with main levels, from which hoisting takes place, 320 feet apart. The main shaft at Kimberley is 2,160 feet deep.

The winning of the diamonds is an interesting process. The blue ground, deposited from trucks conveyed by endless chain haulage, is harrowed as it lies exposed to the disintegrating action of the sun and rain, on the depositing floors. These have a hard and level surface, and at De Beers cover an area of about two square miles. The blue ground, spread to a thickness of nine inches, lies exposed for about six months before it is thoroughly disintegrated. Even at the end of that time, there is some 14 per cent. of the material that is not acted on, being so hard that it has to be crushed. When the disintegration is complete, the material is hauled to the washing machines, where it is raised by a lift, and passed through a revolving cylindrical screen with 1 inch holes. The lumps pass out for further treatment, whilst the pulverised blue ground passes into shallow annular pans in which are mounted revolving toothed arms. The diamonds and heavier matter pass to the outside, whilst the lighter waste material flowing towards the centre, is discharged. The entire gear is driven by electric motors. The concentrates are conveyed in locked trucks to the pulsators which are similar to the jigging machines used in ore-dressing. The heavy material obtained, containing the diamonds was, until recently, taken to the sorting tables, the sorting being conducted first when wet by skilled workmen, and again when dry by native convicts. This tedious procedure was done away with by Mr. Kirsten, who invented the automatic diamond sorter termed the greaser," in which a table built up of five steps covered with a coating of thick grease is vibrated rapidly as the concentrates are allowed to drop on to the top step gradually. The diamonds adhere, whilst the garnets, zircons, mica, magnetite, pyrites, and other minerals are washed off. The diamonds are boiled in caustic soda to clean them. Formerly, out of 192,000 cubic feet of blue ground washed daily at De Beers and Kimberley mines, 160 cubic feet had to be sorted by hand. Now, with the appli

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the period of the agreement with the company. These compounds, of which there are twelve, consist of rows of iron buildings placed along the sides of a large square, which is surrounded by a 10 foot wall. The largest one at the De Beers mine covers an area of about five acres, and affords accommodation for 2,000 natives. The houses which the natives occupy are clean, lofty, airy tenements, with sleeping bunks arranged somewhat as in large steamers. Sanitary regulations are strictly enforced; and an

pipes and cigars, and an abundance of fresh meat. The Kaffirs buy their own provisions and do their own cooking, members of the same tribe frequently clubbing together for this purpose. The compound is also provided with a hospital, dispensary, church, and school.

Next in importance to the four great mines of the De Beers Company, to which reference has been made, is the mine at Wesselton, which was not discovered until 1890. It is worked as an open quarry, and yields clear stones of irregular shape. The extent of the operations of

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35s. 6d. The cost of production per load was 8s. 54d. The Premier mine at Wesselton produced 1,932,140 loads yielding 561,990 carats valued at £941,300. The number of carats per load was 0.30, the value per carat being 33s. 6d. The cost of production per load was 3s. 5d.

In the early days, a good deal of the waste from the mines was used for making up the streets of Kimberley, and, at the present time, the streets are being washed for diamonds, with very remunerative results. Outside Kimberley there are several diamond mines, but none have attained the success of the Kimberley mines. At Jagersfontein, where diamonds were discovered in 1870, the stones are of better quality than De Beers, but the average yield is much less. On the Vaal river, where river washings were extensively carried on; the deposit is similar in composition to that of Kimberley, and is worked as a quarry by two companies. The mineral is screened, and washed and treated on greasers, as at De Beers. The stones are small but of good colour. The most recent development of the South African diamond industry, has been the wonderful discoveries of diamond deposits in

The existence of diamonds and other gems in New South Wales was recorded as early as 1851, but no systematic attempts to work the deposits were made until 1872, and little success attended the industry until 1890. The diamonds occur in the Inverell and other districts in old Tertiary river drifts. The diamonds are harder and whiter than the South African ones. The majority of diamonds obtained weigh from 1-6th to 1-5th carat, while the largest vary from 2 to 3 carats. The number obtained per load varies very greatly; the Round Mountain Company at Cope's Creek, in the Inverell district, washed 722 loads for 2,685 carats in 1886, obtaining from six loads the exceptional yield of 1,080 diamonds, weighing 296 carats. In 1902, the Inverell Diamond Fields, Ltd., obtained 4,538 carats from 4,640 loads. The total output of New South Wales was 11,995 carats, valued at £1,1326, and the Malacca Diamond Mines, Ltd. (Fig. 13) are now giving regular returns of 1 carats of diamonds to the load. Another source of diamond supply is British Guiana, where, in 1901 there were produced 91,286 diamonds, weighing 8,227 carats,

Although known in ancient times, diamonds were for centuries but little used as ornaments. The practice of roughly cutting diamonds is of great antiquity, but it was not until 1456 that Louis van Berghem, of Bruges, discovered the art of cutting into facets. The double-cut brilliant, now the usual form, was introduced by Vincenti Peruggi, of Venice, at the end of the 17th century. The centre of the diamondcutting industry is Amsterdam, where some 12,000 workmen are employed. Of late years Amsterdam has lost the monopoly it formerly possessed, and more diamonds are cut in New York, London, and Antwerp. The finest stones are those from India. The oldest known and largest, the Great Mogul, was seen by Tavernier in Delhi, in 1665. It was subsequently lost. Its weight was 280 carats, and the uncut stone must have weighed 787 carats. The Orloff diamond (193 carats), mounted in the Russian Imperial sceptre, and the Kohinoor (originally 186 carats) are also of Indian origin, and similar in form. The latter was recut in 1852 with a reduction in weight to 106 carats. The most beautiful cut brilliant is the Regent or Pitt diamond in the possession of the French Government, which was recut in London in 1717, and thereby reduced in weight from 410 carats to 1363. The Florentine diamond now in the possession of the Emperor of Austria is 133 carats in weight and cut in the usual manner. The Nassak diamond, 893 carats, is of an irregular triangular shape. The Pasha of Egypt diamond weighs 40 carats. Every year we hear of new discoveries in South Africa of diamonds of remarkable size. The largest, the Excelsior, was found in 1893 at Jagersfontein, and weighed 971 carats. The yellowish De Beers diamond, 428 carats, gave when cut a brilliant of 288 carats. coloured diamonds, the Hope blue diamond (44 carats) and the pale green diamond (40 carats) at Dresden are the most celebrated. The quantity of diamonds the world has produced up to the end of 1901 may be estimated as follows:

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rich in corundum. A large number of localities at which it occurs are mentioned in Mr. T. H. Holland's monograph published by the Geological Survey of India. There are large deposits of the common form of this mineral, emery; and the most highly prized specimens of its transparent red variety, the ruby, have been obtained from Burma, whilst the mines of Kashmir are noted for the size and transparency of the blue variety, the sapphire. Until recently nearly all the known occurrences of corundum were in detrital material. Mr. C. Barrington Brown was the first to prove the existence of the ruby in situ in crystalline limestone, and in conjunction with Professor Judd he has published a masterly memoir on the subject in the "Philosophical Transactions of the Royal Society." The most important locality is near Mogok, in Upper Burma. The rubies occur in a clayey mass, an alteration product of a coarsely granular marble. Sapphire, spinel, and tourmaline are also met with. This

marble appears to have been derived by contact metamorphism from a dolomite limestone of Upper Carboniferous age. Such limestone still stands unaltered in many places, and in others has been altered into marble by up-bursts of eruptive rock. The clay containing the rubies lies at the side of valleys and fills wide cavities. The stones found are much worn and corroded on the surface. The Burma Ruby Mines Co., Ltd., founded in 1889 with a capital of £150,000, is now, after many difficulties, obtaining very satisfactory results. In the year ending February 28th, 1902, a dividend of 17 per cent. was paid. During the year 1901 the Company washed 947,444 loads of gem earth at a cost of 10.29d. per load. The production included 210,784 carats of rubies, 9,786 carats of sapphires, and 10,241 carats of spinel. The methods of mining for the ruby in Burma are suited to the three modes of its occurrence in the limestone, in hill detrital material, and in the alluvial deposits in the valleys. In the quarries blasting is unsuitable as it injures the gem stones. The dirt is raised by endless ropes from quarries 50 feet deep. Stones of greater weight than four carats are of such exceptional occurrence that they command fancy prices. The largest known were brought from Burma in 1875 and weighed 37 and 47 carats respectively. They are said to have been sold for £10,000 and £20,000. English cut sapphires under one

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