DIAMANTINA (de-a-man-te'nb.), a town in the Brazilian province of Minas A diamond crystallizes in the cubic or monometric system, its common form being the regular octahedron or a modi fication of it. The bases are often curved and the general form of the crys tal is more or less rounded. The surface of the diamond frequently exhibits strip and triangular impressions, while the in terior may contain microscopic cavities and various inclusions, often black car bon. It is the hardest substance known; but in spite of this hardness it is very brittle and cleavable; specific gravity, 3.52. It is generally colorless, but some times tinged pink, red, orange, yellow, green, blue, brown, or black. Blue, red, and green are exceedingly rare colors. Light yellow, straw, and brown are the most common colors; rich yellow and browns are also highly prized. Some bluish-white Brazilian diamonds are phosphorescent in the dark after ex posure to the sunlight. Originally dia monds were preserved in their natural form, but in 1456 Louis de Berguin of Bruges discovered the art of polishing them on rotating disks with diamond dust. These circular disks, about 10 meters in diameter, are at the present time of soft steel covered with diamond dust and oil, and made to revolve at 3,000 revolutions a minute. This gives the diamonds the artistic smooth sur faces and sharply defined edges. The process is slow and tedious, and requires great skill to produce fine results. Until a few years ago Amsterdam was the great diamond-cutting center of the world, but the finest cutting is now done in the United States, and in a great measure by machinery. As to the cut ting process: Diamonds are, first, cleaved; that is, along the line of cleav age of the stone a tiny cut is made by rubbing the stone with another dia mond at the point where it is desired to cleave it, then a dull knife-edge is placed in the cut, and a sharp blow will sepa rate the stone on a cleavage plane. Secondly, diamonds are cut by rubbing two diamonds together, the stones being cemented with shellac to two pieces of wood or handles which are held in the hands, and rubbed together till they are of the desired form. This also has been
superseded partly by an American ma chine.
Diamonds of from 1 to 22 carats each have been found in 24 localities in the United States, mapped by Kunz for the United States Geological Survey. The combustibility of diamonds was proved in 1694 by Averani and Targioni with the aid of burning glasses. That dia monds turned to carbonic acid when burned was proved by Lavoisier in 1772. In 1867, in the S. of Africa, John O'Reilly, a trader and hunter, reached the junction of two rivers, and stopped for the night at the house of a farmer named Van Niekerk. Children were play ing with some pebbles they had found in the river. O'Reilly took one of these pebbles to Dr. Atherstone, at Cape Town, who said that it was a diamond of 22% carats. It was sold for $3,000. Niekerk remembered that he had seen an im mense stone in the hands of a Kaffir witch-doctor, who used it in his incan tations. He found the man, gave him 500 sheep, horses, and nearly all he pos sessed for the stone, and sold it for $56,000. This was the famous "Star" of South Africa. It weighed 84 lb, carats in the rough, and was found to be a gem quite the rival of an Indian. stone in purity and brilliancy. After it had been cut it was bought by the Earl of Dudley, and is now known as the Dudley diamond. By 1869, parties in ox-wagons had worked their way over the plains to the Vaal river. Soon a tented city of 12,000 or more foreigners grew at Pniel and Klipdrift, on the op posite banks of the stream, where dia monds were found plentifully. The mines at Kimberley, 600 miles from Cape Town, are the richest in the world. The output of a single mine, the "Kim berley,' is $4,000,000 annually, and within 10 years this district has yielded about $58,000,000 in dividends. Ninety five per cent. of all the diamonds pro duced in the past 20 years came from South Africa.