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PRECIOUS STpNES.
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ficecl from careless handling, or from not understanding
properties. Cleavage, an important quality in diamond-cutting, is always j
parallel to the faces of the octahedron, and, whatever shape it assumes, it can be split into that figure. The magnifyine power of this gem is superior to that of glass, which has lea to its use, in some instances, for microscopic lenses, thougfl it is said to be difficult to make them perfectly accurate. ] A summary of the properties of the diamond is as follows:
Hardness, io; specific gravity, 3.55 ; cleavage, perfect; refraction, simple; transparent to opaque; combustible; infusible; frangible ; phosphorescent ; great power of refraction ; dispersive power ; remarkable lustre and play of colors ; positively electric by friction ; non-conductor of electricity ; does not polarize light. Classification. — Dieulafait recognizes this precious stone
under three different molecular states : First, crystallized — the most usual form, and the one employed in jewelry ; second, crystalline, or imperfectly crystallized, as bort, which is excessively hard, far exceeding the ordinary diamond in hardness, and used for powder ; third, amorphous or uncrystalline, an opaque, steel-gray mass, called carbonado, used for polishing. It is sometimes of a granular structure, imperfectly crystallized, porous, dense, or massive, with a hardness equal to and even surpassing the crystallized form, and when burned, it leaves a residuum of clay and other substances. It was formerly believed that the diamond was a kind of
rock-crystal, and the latter has sometimes been mistaken for it, but a knowledge of crystallography would have prevented such an error. Quartz crystals are hexagonal, whereas those of the diamond are eight or twelve faced, though the primitive forms are sometimes varied and complex. The normal shape |
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