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-•61 Silkems Genus. a mixed colour of bluiflj green and golden yel low. Its luftre, 3.4. Tranfparency, 3.4. Its fra&ure conchoidaf. Its hardnefs, 10. Sp. gr. 3,698 to 7,719, U *4 . ' I2th Species. Chryfolite. Its moft ufual colour is yellovvifh green, mixed with browij, fometimps verging to the ojive green, and fometimes to pale yellow, nrixed wich grey, feldom allied to reddiih brown, or grafs green. Its internal luflre, 3.4. Tranfparency, 4.3. It is found partly in Iharp uneven indentcd fragments, ofien rounded grains, and partly in mutilated cryftals, which feem' to derive from right-angled quadrangular priims, whofe angles were truncated. Its furface has a fine fplintcry or fcaly appear- ance; but fuch of the cryüals as have not been injured by fiiöion have their broadelf fides flreaked lengthways. Where the furface has not fufFred by attrition, it has a conliderable luftre. Itsfrafture, in every diredtion, is conchoidal. Fragments, 3. Its hardnefs from 9 to 10. Brittle. Sp.gr. from 3,340 to 4,410. Mr. Werner adds, that no fione, whofe tlenfity is inferior' to 3,300, or ' iuperior to 3,450, is a chryfolite. It is infufiole at 1 50 0 , but lofes its tranfpa rency and becomes blackilh grey. By pure air it