364 FELSPAR FAMILY. Constituent Parts. Silica, Alumina, Potash, Oxide of Iron, 68.0 15.0 14.5 0.5 98.0 Klaproth, Beit. b. v. s. 18. Geognostic and Geographic Situations. It occurs imbedded in a porphyritic rock in the Sie- bengebirge; also in a rock composed of white felspar, and very small blackish-brown scales of mica, and fine dis seminated magnetic ironstone, in the Drachenfels on the the Rhine. It is an inmate of the floetz-trap rocks of the Bohemian Mittelgebirge; and has been noticed in the porphyritic pumice of Hungary ; and the floetz-trap and pitchstone rocks of Scotland. It is also said to occur in veins in Dauphiny, along with axinite and epidote ; and in the lava of Solfatara. Glassy Felspar is distinguished from the other mine rals of the felspar species, by its white colour, splendent vitreous lustre, transparency, and the frequent rents or fissures with which it is traversed. Observations. Second