DIAMOND posits which are worked for gold, sometimes ,1 to loose pieces of brown hematite, and sometime* in H glomerate of quartz , n y. rrm.-nted ly ferruginous clay ; but it is not certain in what geological forma- tion it orL'iriated. (Jeiierally in regions where .MI,. ml is found there also occurs a lam- inated granular quartz rock, called itacolu- nnntion, and which in thin plates is more or less flexible. According to
- ,is. it is found in Minas Geraes, Bra-
7.], in two different deposits: one, called ho, which is composed of pieces of i quartz, covered by a thin bed of and the other, called cascalho, com- ..f quartz pebbles, united by ferruginous clay, and usually resting on talcose clays, the l.t-injr debris from talcose rocks. The first is said to yield the finest diamonds, and both contain gold, platinum, and magnetic iron. The diamond mines of India have the same character as those of Brazil, the alluvial earth being a conglomerate of more or less ty. which requires to be broken up. The diamond was long known in Asia, in Hin- dostan, Borneo, Sumatra, and in the Ural mountains before it was discovered elsewhere ; the district from Cape Comorin to the bay of Bengal, including the famous mines of Gol- conda, furnishing the world until 1728, when the Bra/.ilian mines were discovered. (See DIAMOM, DISTRICT.) The South African dia- mond tit-Ms were discovered through some children finding a diamond of 21 carats on the banks of the Orange river, in 1868. In 1869 the " Star of South Africa," of 83 carats, md by a (iriqua shepherd; and on the borders of the Vaal river several small stones found early in 1870. Since then the M'.-irdi has increased, until now there are said to be more than 4,000 persons, over an extent of 1,500 sq. m., chiefly in the valleys of the ( r:iriirc and Vaal rivers and at their junction, n lat. 26 and 28 S., and Ion. 24 and 26 E. The diamonds are found, from the sur- face to a depth of To ft., in nn alluvial cal- - earth, with rolled pebbles of quartz, rhal.-.-dony, jasper, and garnets, and decom- Id-pathic and micaceous rocks, resting -iialo. The peculiarity of the n diamond i< the givat number of stones of 80 carat* and upward, with a preponderance nt. of yellow-tinted. The comm. r- "f such a quantity of yellow dia- mon.U comirii.' at ,.in-.> on the'market has been to depredate th,-ir value in an extraordinary "W stones being now but one fourth il,,- pri.v tli.-y , tv 1i,- years since; nan iite .. n .- half their pre- ralue. 'Iln- who],, of the South African bout 17. "00 sq. m., wasan- 'lony of (in-nt liritain title of Griqualand. Reoenfly the ! to i, t . profitable. Of tin- mm,-* arc abandon. -d. few foil number of workmen; and even the South African fields are said to be declining. In the United States, diamonds have been dis- covered in Rutherford co., N. C., and in Hall co., Ga. ; also at Paris mine, Franklin co., N. C. ; and at the village of Manchester, opposite Richmond, Va. ; in California, at Cherokee ravine, in Butte co. ; at Forest hill, El Dorado co., one of 1 carat, and at French Corral one of 1 carat, have been found. In Australia, they have been met with in the valley of the Turon, in the bed of the Macquarie river, at Victoria, and at Fremantle in Western Austra- lia. Diamonds are found of various colors, as well as colorless and perfectly transparent. The latter are most esteemed, and are distin- guished as diamonds of the first water from their semblance to a drop of clear spring water. When of a rose tint and of clear water, they are also highly valued. A yellow shade is ob- jectionable, as is a cinnamon color, a stone having these rarely being clear and sound. Next to the rose, a green color is the least ob- jectionable ; many very fine diamonds have this tint ; and some are found of a bluish color, and some black. For the valuation of diamonds an arbitrary rule has been given, which is, however, little regarded in actual sales of the most costly of these gems. Purchasers for such being few, the only real rule adopted, as in the sale of many other commodities, is to demand the highest price there is the least probability that one may be induced to pay. The mere statement of the rule is sufficient to show its indefiniteness. It is to multiply the square of the weight in carats by a sum vary- ing according to the state and quality of the stone. If clear and of good shape, this sum was 2 ; if perfect and well cut, 6 or 8 for the brilliant or rose, but a lower figure for the table. The rate is now $50 in place of the 2 above, and a specimen brilliant is worth $200. For diamonds of moderate size the rates vary as little as those of exchange between coun- tries. They follow from the natural propor- tions in which diamonds are found. Diamonds weighing over 10 carats have a higher propor- tional theoretical value than the smaller sizes; yet the latter can commonly be sold at higher proportional rates, on account of the few pur- chasers for those of large size. In the great sale of jewels in London in 1837, on the dis- tribution of the Deccan booty obtained by the army of the marquis of Hastings, the splendid Nassuck diamond, weighing 357 grains, and of the purest water, brought only 7,200. In December, 1858, 33,000 was paid for a stone weighing 61 carats, and 15,000 for a pair of drop-shaped diamonds for earrings. The finest gems of commerce are now in great part sup- plied by the old jewels of Portuguese, Spanish, French, and English families, the proportions from each nation being in the order named; and the best market for them is now the Uni- ted States. The origin of the art of cutting j diamonds in a scientific manner is ascribed to Louis Berquen in 1456, who established a
