Diamond. - 393 'first APPENDIX. Diamond. IXS colour is moft commonly pale grey, which often pafles into the yellow, fometimes citron yellow, t'eldom rofy red, Hill mbre rarely green or blue, but very often pale brown, or co- lourlefs. It occurs moft commonly in rounded grains, feldomer in double quadrangular pyramids, or flat double triangulär pyramids, whol'e edges are convex, &c. Its external luftre cafual, internal, 4. Its tranfparency, 2.3.4. Its fra&ure foliated. Fragments, 4. Its Hardnefs, 20. Its fpec. gravity from 3,44 t° 3,55. It gives but a fingle refra&ion. , ' In a heat of 35 0 or 40°, it confumes and burns like an infta nmable iubftancc; hence fome think it a very pure fpecics of coal. No acid has any efte£tonit. SECOND