28a Siliceous Genus. 2ift Species. Staurolite, or crofs ßone of St. Andreafberg, In the Hartz». Kreutz Cryftal of the Germans. Iiyacinth Blanche of 2 Rome, p. 299. Of this ftone there are two varieties. The fe- cond is very fcarce, having occurred but once. The colour of the firft is milk white i of the fecond, brownifh grey. Their fhape is that of tivo quadrangular tables or flat quadrangular prifms, bevilled at the edges^ and lnreriedfing each other at right angles. Some difference may take place as to the form of the edges, and the angle of interfe&ion. ihecryftals of the 2d variety are moft com« monly fulcated. The luftre, both external and internal, is va-. nable. Of the firft generally z-, and of the waxy kind, that of the fecond pearly; and fomewhat lfronger than that of the firft. T ranlparency, 1.2.3. The fradture of both is fohated, Fragments, 3. Hardnefs, brittle. Gp. gr. of the firft, z >355'> »f the fecond, 2,361. Gradualiy heated, both decrepitate and lofe 0,15 or 0,16 of their weight, and' as fome fay, flightly irttumefcef, and then fall in powder! This powder is infufible at 150°, but by pure air is converted into a white enamel. Mineral alkali fluxes both varieties into a frothy enamel; that of the firft is white, that of the * 2 Bergbau, p. ?.j. f 2 Lempe jVlag. p. 59. 2 fecond