THE NONMETALLIC MINERALS. 167 



has arisen a constant and growing demand for black diamonds, or bort, 

 for the cutting edges of diamond drills, and to a less extent for teeth 

 to diamond saws. (Specimens Nos. 53668 to 53670, U.S.N.M.) 



According to a writer in the Iron Age 1 the crystallized diamond is 

 not suitable for these purposes owi ng to its cleavage property. The best 

 bort or "carbonado" comes, it is said, from Bahia, Brazil, where it is 

 found as small, black pebbles in river gravels. The ordinary sizes 

 used for drills weigh but from one- half to 1 carat, but in special cases 

 pieces weighing from 4 to 6 carats are used. It is stated that the 

 crowns of large drills, 10 inches in diameter, armed with the best 

 grade of carbonado, are sometimes valued as high as $10,000. 



BIBLIOGRAPHY. 



M. BABINET. The Diamond and other precious stones. 



Report of the Smithsonian Institution, 1870, p. 333. 

 A DAUBREE. Annales des Mines, 7th ser., IX, 1876, p. 130. 



Remarking on the occurrence of platinum associated with peridotites, he calls 

 attention to the fact that Maskelyne had shown the diamonds of South Africa 

 and Borneo to occur in a decomposed peridotite. 



ORVILLE A. DERBY. Geology of the Diamantiferous Region of the Province of Parand, 

 Brazil. 



American Journal of Science, XVIII, 1879, p. 310. 



Geology of the Diamond. 



American Journal of Science, XXIII, 1882, p. 97. 

 H. COHEN. Igneous origin of the Diamond. 



Proceedings, Manchester Literary and Philosophical Society, 1884, p. 5. 

 H. CARVILL LEWIS. The Genesis of the Diamond. 



Science, VIII, 1886, p. 345. 

 GARDNER F. WILLIAMS. The Diamond Mines of South Africa. 



Transactions of the American Institute of Mining Engineers, XV, 1886, p. 392. 

 ORVILLE A. DERBY. The Genesis of the Diamond. 



Science, IX, 1887, p. 57. 

 Discovery of Diamonds in a Meteoric Stone. 



Nature, XXXVII, 1887, p. 110. 

 Diamond Mining in Ceylon. 



Engineering and Mining Journal, XLIX, 1890, p. 678. 

 A. MERVYN SMITH. The Diamond Fields of India. 



Engineering and Mining Journal, LIII, 1892, p. 454. 

 OLIVER WHIFFLE HUNTINGTON. Diamonds in Meteorites. 



Science, XX, 1892, p. 15. 

 Diamonds in Meteoric Stones. 



The American Geologist, XI, 1893, p. 282. (Abstract of paper by H. Moissan, 

 Comptes Rendus 1893, pp. 116 and 228.) 

 HENRI MOISSAN. Study of the Diamantiferous Sands of Brazil. 



Engineering and Mining Journal, LXII, 1896, p. 222. 



HENRY CARVILL LEWIS. I. Papers and Notes on the Genesis and Matrix of the 

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The Geological Magazine, IV, 1897, p. 366. 

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Nature, LV, 1897, p. 325. 



1 Volume XXXVI, December 24, 1885, p. 11. 



