246 Siliceous Genus. hardnefs was, 12. Iis fp. gr. 2,755 *. When heated it aTrafted albes ana other light bodies like rournraline; ir cven became eledtric by fric- tion, and when fo attradted fine ironfihngs. It was intufibie per Je, nor hr.d borax, or microcof- mic falt any eße£> on ir, but mineral alkali fuled it inro an opake opalefcent mafis without cffervei- cence. Bv bis experhncKts it appcais to confift chieflv of filex, with a ferv particles of’ calx of iron and lime. 2 Berl. Ikob. 256. 2d Species. Amethyft. Its mofl ufual colour is viokt blue of different degrees of intenfity, alfo milk white, grey, and very rarely olive or grafs green; often ftriped vvirh two colonrs Its fiiape is generally that of hexahaedral pvra- mids, yet often occurs in blunt-edged pieces. Its internal 1 ult re, fometimes ferong, fomeiimes weak and very weak. Its tranfparency, 2 to 4. It caufcs a double refradtion. When its lußre is ftrong, its fraclure is con- choidal, when weaker fplintery, when weakell: intermediate between the fplintery and the coarfc diverging librous. * The bonk fays 1,755, hat I bcüeve this mit ft be a re if- takeof 1 he preis, otherwiie the aiuhor wo-uld bavcnctictd a c rcutnftance lu icmarkabie. It
