Quartz familv. It is brittle, and easily frangible. Specific gravity, 1.917, Santi. Chemical Characters. It is infusible before the blowpipe without addition. Constituent Parts. Silica, - - 94 Alumina, - 2 Lime, - - 4 100 Santi. Gcognostic and Geographic Situations. ' It was discovered by the late Dr Thompson on the surface of weathered granite at the foot of the hill of Santa Fiora, in the island of Ischia: it has also been found on volcanic tuff and pumice in the Vicentine. / Observations. According to Dr Thompson it is a volcanic production. The silica, he supposes, was held in solution by means of soda, aided by the high temperature of the vapours which exhale from the bosom of the earth in volcanic countries by natural apertures, named fumaroli. p, Hyalite.