In hardness it is nearly equal to adamantine spar; and this property has rendered it an object of great request in various arts. It is employed by lapidaries in the cutting and polishing of precious stones; by opticians, in smoothing the surface of the finer kinds of glass, preparatory to their being polished; by cutlers, and other manufacturers of iron and steel instruments; by masons, in the polishing of marble: and, in their respective businesses, by locksmiths, glaziers, and numerous other artisans. For all these purposes it is pulverized in large iron mortars, or in steel mills; and is afterwards separated, according to the several degrees of fineness that are required, by washing it in water, and suffering the grosser particles to deposit themselves. By this operation the finer particles, which remain suspended in the water, and which are obtained by decanting the water off, and suffering it to stand for a considerable time, are separated. The particles first deposited are again ground, and again agitated in the water, to separate the finest. By these successive operations the emery is reduced to a powder so fine that, when rubbed between the fingers, it communicates no sensation whatever of grittiness. In general those particles only of the emery which remain suspended in the water, after it has stood about half an hour, are used to polish metals. 59. _ADAMANTINE SPAR, or IMPERFECT CORUNDUM, is a very hard and nearly opaque stone, which varies much in colour, but is chiefly grey, with a greenish, brown, or bluish tint._ _It is usually found in the form of six─sided prisms, but it sometimes occurs in shapeless masses, has a foliated texture, and is about four times as heavy as water._ The name of adamantine spar was given, by the British lapidaries, to this substance from its hardness being nearly equal to that of the diamond. It was originally discovered among the granite rocks of China; but it has since been found, and in greater purity, in Bengal and Ceylon. In a powdered state this substance has long been used by the artists of India and China for the cutting and polishing of precious stones, and even of the diamond; but, though it will in some degree operate upon that gem, it is not sufficiently hard to bring out the peculiar beauty of it in a degree at all comparable to that which is effected by the European lapidaries with diamond powder. The Chinese also use adamantine spar for polishing steel, and in the composition of the finer kinds of porcelain or earthenware. For the cutting of seals and precious stones European workmen consider it preferable to emery; but, for minute engraving, it is much inferior to diamond powder. 60. _CHRYSOBERYL is a gem of yellowish or brownish green colour, harder than quartz (76), and sometimes transparent; but often only semi─transparent, in which case it exhibits a bluish light, floating in the interior of the stone._