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3^6 CLAY GENUS-, other bevilled, the bevilling planes fet oil the two oppofite lateral edges. 3. Similar prifm at one extremity flatly acumi- minated by three planes, which are fet on the alternate lateral edges, on the other bevilled, the bevilling planes fet on the op pofite lateral edges. Cryftals fmall and middle iized. Surface fmooth. Luftre of the principal fradlure fplendent, crofs frafture gliftening and vitreous. Principal fradlure perfectly ftraight foliated, with a double obliquely interfering cleavage ; crofs frac ture fine grained uneven approaching to fmall con- choidal. Fragments generally indeterminately angular, fome, times alfo rhomboidal. Always opaque. Semi-hard. Pretty brittle. Eafily frangible. Not particularly heavy. Specific gravity—3> 2 5°» Hauy.—From 3,150 to 3,2 2 °> Reufs—3,333, Kitnvan. / Chemical Character. Before the blow pipe it melts fnto a black glafs* but is more refraftory than common hornblende. Constituent 1