Bißinßive Charaftersi Üpecular, prefenting a flat poliflied furfdce like ä mirror. Cellular, prefenting cells formed of lamin* Crcrfling each other. Perforated, traverfed with round holes. Conoded. beterminate. Under this head ate comprehended the various orms of cryftallized fubflances, refulting from e aliemblage of a determinate nuriiberof fides. Ine variedes of form which cryftallized oc les prefent I fhall not attempt to enumerate, and fo rnuch the lefs as I think their detail of very httle ufe. Thofe who wifti for more infor- mation on this head may confult Rome de Lifle, Mr. Werner, and an excellent Diflertation by Mr. Wideman, in the 4th volume of the Berlin Ob- lervations. ^ A furface on which very minute cryftals abound is called drvfy. Luftre. Luftre is the glofs, and often brightnefs, which foflils difcover, fometimes on their external fur face, but more frequently on their internal furface, when frelh or broken. Of this luftre Mr. Wer ner diftinguifhes various forts; the metallic> the pearly, the waxy, that of greafe, the glaffy i and the common. When no particular fort is men- tioned, it is underftood to be of the common kind. 7 There