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 substance yet known to mankind.
Industrial diamonds can be mined from natural deposits or they can be produced synthetically. Among naturally occurring diamonds, three varieties exist : ballas, boart and carbonado.
Ballas, or shot ball 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 America. Brazilian ballas is said to be the harder of the two.
Boart 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 diamonds, is crushed in steel mortars and graded into abrasive grits of various sizes. 75 % of the world's crushing bort comes from Congo (Kinshasa). Its chief use is in the manufacture of grinding wheels for sharpening cement 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, etc.