Page:The New International Encyclopædia 1st ed. v. 06.djvu/238

DIAMOND. as 'bort' or 'carbonado.' which is unsuitable for gems, is exlonsively used on the cutting edge of drills lor tunneling and prospecting.

Dcci KRK.NiK. Previous to the discovery of the Brazilian mines in 17-7. diamonds were found chielly in India and Borneo. In India they have been obtained near Kadai)a, Karniil. and Hellari in -Madras Presidency; near Xagpur, in the Central Provinces; and at Panna, in Bundel- khand. The famous Oolconda was a market in .Madras Presidency where the diamonds were col- lected from the mines. Formerly the diamond- mining industry gave employment to a large nunilier of people, but. owing to the gradual ex- haustion of the deposits and the crude methods of working, it has steadily declined. The diamond- mines of Borneo, which supply about 3000 carats annually, are located in the western part of the island near Pontianak. The Brazilian diamonds come from a small district within the States of Haliia, Minas Geraes. Goyaz. and Matto Grosso. being foinid for the most part in placers. Dia- mantina, Bagagem. and Abaete in Minas Geraes are the principal localities for gem-stones, and Lengoes. Sincorfl. and Santo Ignacio for carbo- nados. The alluvial deposits consist of water- worn quartz pebbles, and ferruginous clay, car- rying rutile, lienuitite. ilmenite, and other minerals besides the diamonds. In one locality (Bagagem) the stones are found in a weathered, decomposed phyllite; they are also known to oc- cur elsewhere in conglomerate. The total output of the Brazilian mines up to the year 1800 lias been estimated by one authority at 13.105.000 carats. The most valuable specimen from this source is the "Southern Star." found in 1854, which weighed "254 carats in the rough, and 124 carats after cutting. The South African dia- monil-fields yield about 98 per cent, of the total product. Their discovery in 1867 came from the purchase of a stone that had been picked up by the children of a Boer farmer, and which was subsequently sold in Paris for $2500. The dia- monds arc found in both river diggings and dry diggings. River diggings occur along the Vaal River from Potchefstroom down to the conflu- ence with the Orange, and up the latter river as far as Hopetown. Mining is conducted in a similar manner to gold-washing, the operations usuall,v being on a limited scale. The dry dig- gings are in Griqualand West, on the borders of the Orange River Colony, about 040 miles north- east of Cape Town. They comprise a number of small areas of circular or oval form, ranging in diameter up to one-fourth of a mile. Origi- rially the areas were divided into small claims. each owned and operated independently, but they are now worked by a single company, the De Beers Consolidated Mines. Limited, whose head- quarters are at Kimberley. The mines are opened on a large scale, and yield enormous profits. It is stated that the output from 1867 to 1897 wa^ over 33.000.000 carat*, or about 7l{. tons, valued after cutting at .?45O.O0O.O00. In the fiscal year 1901 the De l?eers Company received $23,144,225 from sales of rough dia- monds. The South African di.nmonds in the average do not equal the Brazilian for purity, although some of the most valuable stones, re- markable for quality as well as for size, have been found in these mines. Other countries where diamond-i are known to occur are the United Slates, British Guiana, Russia, China, Sumatra, and Australia. In the I'nited States there arc no deposits, so far as discovered, of sullicient value to warrant mining ojicrations, the stones being found only occasionally in alluvial mate- rials and drift. More than tifty specimens have been identified, of which the largest, weighing nearly 24 carats, was found at JIanchester, Va.. in 1S55. Their occurrence is generally confined to the regions of the southern Appalachians, the Great Lakes, and to the Coast and Sierra Xevada ranges of California and Oregon. The diamond-fields of British (iuiana are about 250 miles up the Mazaruni River, and. while new, they give sonu' promise of future importance. Xew Soutli Wales produces about 25.000 carats annually from alluvial washings near Mudgee, and on the Macquarie River. In Russia, dia- n;onds occur on the western slopes of the Irals, and are obtained in the washing of sands and gravels for gold.

Origin or l)i.Moxns. The problem as to the origin of the diamond, once a favorite subject of speculation, has been studied recently by scien- tists with some success. In this connection, the South African fields are most significant. As previously stated, the deposits are circular or oval in form, and it has been found that they are inclosed by a wall of carbonaceous shale. For a considerable distance below the surface, the deposits consist of a yellowish, friable mate- rial called by the miners "yellow ground,' but when, with depth, the limit of atmospheric weathering has been reached, they pass into a partially serpcntinized olivine-pyroxene rock of igneous character, known as 'blue ground.' These facts indicate that the deposits occupy the vents or pipes of ancient volcanoes, and it is there- fore probable that the presence of the diamond i.^: connected with volcanic activity, the stones either having been brought up from the interior of the eartli, or having been formed in place under the influence of the molten rock in con- tact with the carbonaceous .shale. The French geologist De Launay has argued that the dia- monds have come up from below. This view seems to be supported by the fact that their occurrence is apparently independent of the in- closing rock, whether this be the car1>i«naceou» shale found at the surface or the underlying dia- base and quartzite. The conditions necessary for the crystallization of carbon in the form of diamond would seem to be intense heat and great pressure, such as exist during the forma- tion of igneous rocks. Successful attempts to reproduce these conditions artificially have been carried out by Professor Moissan of Paris, and also by the Knglish chemist Professor Crookes. The method employed consists in heating pure jircpared carbon and iron in an electric furnace. ]?y sudden cooling of the molten iron, the surface contracts and exerts a powerful pressure upon the interior mass. When cold, the iron is dis- solved in acid, and small black particles remain which exhibit the properties of genuine dia- monds.

V.m.it:. The value of gem diamonds cannot be determined by absolute standards. Weight, cut, brilliancy, color, and perfection of the atones are factors that must l>e considered in c^timnting the value, which is. moreover, subject to fluctuation. Colorless stones bring higher price's than off-colored stones, but if decided tints of red. blue, or gieen are present they may increase