INDUSTRIAL DIAMOND

any diamond that is designated for industrial use, principally as a cutting tool or abrasive. In general, industrial diamonds are too badly flawed, irregularly shaped, poorly coloured, or small to be of value as gems, but they are of vital importance in the modern metalworking and mining industries. Their utility stems from the fact that diamond is the hardest natural substance known. Industrial diamonds can be mined from natural deposits, or they can be produced synthetically. Among the naturally occurring diamonds, three varieties exist: ballas, bort, and carbonado. Ballas, or shot bort, is composed of concentrically arranged, spherical masses of minute diamond crystals. Ballas is extremely hard, tough, and difficult to cleave. Principal sources are Brazil and South Africa. Brazilian ballas is said to be the harder of the two. Bort is a gray to black massive diamond, the colour of which is caused by inclusions and impurities. The name is also applied to badly coloured, flawed, or irregularly shaped diamond crystals that are unsuited for gem purposes. Drilling bort is composed of small, round stones averaging 20 to the carat and is used in diamond drill bits. Crushing bort, the lowest grade of diamond, is crushed in steel mortars and graded into abrasive grits of various sizes; 75 percent of the world's crushing bort comes from Congo (Kinshasa). Its chief use is in the manufacture of grinding wheels for sharpening cemented carbide metal-cutting tools, but it also is used as loose grains suspended in oil or water for lapping and polishing. Carbonado, known in the trade as carbon, is black, opaque diamond. It is as hard as crystallized diamond but less brittle, and, because its structure is slightly porous, it has a lower specific gravity (3.51 to 3.29). Carbonado has no cleavage and therefore is valuable for use in diamond-set tools. It usually occurs in small masses in the diamond-bearing gravels of Bahia, Brazil, and in Borneo. Rock-coring drills, widely used in exploring for new mineral deposits, are made by mounting diamonds around the rim of a hollow metal drill crown. Other important applications include saws for cutting rock and other hard materials, lathes and other types of cutting tools, glass cutters, phonograph needles, hardness testers, and wire-drawing dies. See also synthetic diamond.