The Diamond

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The Diamond, mineral form of carbon, valued as a precious stone, and also used for various industrial purposes. Diamonds occur in various forms, including the diamond proper, bort, ballas, and carbonado. Bort is an imperfectly crystallized diamond, extremely hard, and dark in color. The term bort sometimes is applied also to minute fragments of gem diamonds. Ballas is a compact, spherical mass of tiny diamond crystals of great hardness and toughness. Carbonado, sometimes called black diamond or carbon, is an opaque grayish or black form of diamond with no cleavage, the property of a crystal to split along a definite plane. Carbonado, ballas, and bort are all used industrially, in lapidary work, and for the cutting edges of drills and other cutting tools. The name diamond is derived from the Greek word adamas (“invincible”), which was probably applied by the Greeks to any hard stone. The first distinct and undoubted reference to diamonds occurs in Roman literature of!
the 1st century AD. The diamonds known to the Romans undoubtedly came from India. Until the 18th century India was the only known source of the stones, and they were believed to be found only in the fabled mines of Golconda. Golconda was in fact the market city of the diamond trade, and gems sold there came from a number of mines. In 1726 diamonds were discovered in Brazil, and in 1866 in South Africa. The latter area is now the chief source of gem diamonds.
Diamond is the hardest substance known and is given a value of 10 in the Mohs hardness scale, devised by the German mineralogist Friedrich Mohs to indicate relative hardness of substances on a rating scale from 1 to 10 . Its hardness, exhibited in its resistance to scratching, is not a constant quantity, but varies in every diamond with the crystallographic direction, being greater on surfaces parallel to the octahedron than on those parallel to the dodecahedron planes. Moreover, hardness on the same...