38 Dißindive Characlers, a knife, as fluors, zeolytes, calcareous fpars, ba- falts, &c. 3° he calls tendet or foft, thofe that may eafily be fcraped by a knife' but not by the nai], as barofelenite, mica, ferpentines, &c. 4° he calls very foft or ten'der, thofe that may be fcraped by the nail, as flcatites, gyplum, talc, &c. I diftinguiflh the various degrees of hardnefs by figures. 3. denotes the hardnefs of chalk. 4. a fuperior hardnefs, but yet what yields to the nail. 5. that which will not yield to the nail, but eafily and without grittinefs to the knife. 6. that which yields more difhcultly to the knife. 7. that which fcarcely yields to the knife. 8. that which cannot be fcraped by a krilfe but does not give fire with fteel. 9. that which gives a fevv feeble fparks with fleel, as bafidt. xo. that which gives plentiful lively fparks, as fiint. ^ The fuperior degrees are difcovered by obfer- ving the order in which (tones cut each other. Under this head all’o, ßexibilily and claßicity m a y be noticed. Dcnßty. This is found by taking the fpecific gravity of flones, &c. in diftilled water at the temperature of from 59 0 to 64° Fahr. As the temperature of 62 0 , the true tempera ture for taking lpecific gravities, does not always 7 prevail,