2^4 Siüceous Genus. It is found generally in roundilh grains, moftly inferted in other ftones; but fometimes in large mafies, never yet cryftallized. Fradture, conchoidal, approaching to the un- . even, feldom imperfeftly foliated; and then it is not certain that it is not different ftone; or, per- haps, a>variety of the iame *. When large, it prefents fmall-grained diftinft concretionsealily feparable. Its hardneis, 9. Brittle. Sp. gr. from 2,96 3> 22 5* It eafily withers by expofure to the open air. By the experiment of Mr. Voight and Mayer, it is fufible into an enamel in a heat of 1 co° or 160 0 . * Hitherto it has been found only in bafalts or traps, and not in wacke, or amygdaloids; yet Mr. Lievre affines us, he detefted it in fome potftones on the Pyrenees. 30 Koz. 397. 1 his ftone is attacked by digeltion in nitrous acid; and its ferruginous part taken up; but chryfolites arenotaffedted by this acid; and thus we have a fufficient criterion whereby to diftin- guilh them. i4th Species, t Obfidian. Icelandic agate of fome, lux fapphire of Hun- gary. * 1 Bergm. Journ. 1792, p. 242; » ItS