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12 FLINT GENUS. Externally its lufire is fhming and gliftening ; & ternally fhining, which fometimes paffes into gliften- ing and fplendent, and is vitreous. Crofs fra&ure intermediate between uneven and frnall, and imperfectly conchoidal; longitudinal frac* ture foliated with a fourfold cleavage: three of the folia or cleavages are parallel with the lateral planed and the fourth with the terminal planes ; and the l 3 ' j teral and terminal cleavages generally interfeft each other at right angles. The cleavage is often vetf imperfeft. Fragments indeterminately angular, more or l e ‘ s fharp edged. \ The maffive is compofed of ftraight and thin colutfj nar prifmatic diftinct concretions, which are form e by collections of prifms difpofed in different dir eC ' tions. , ; Commonly tranfparent, but fometimes paffes ■ tranflucent, and is flightly duplicating. '1 he tran | cent variety has crofs rents. ^ Hard : fcratches quartz ; nearly equal in hardn® to topaz, with which the mountain green variety h a> been often confounded. Eafily frangible. Not particularly heavy. (0 Specific gravity.—26,500 to 27,590, ]Werner.— 2,722, Brijfon.