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252 GYPSUM FAMILY. Externally it is shining, or splendent and pearly: in ternally splendent and pearly. 1 he fracture is foliated, with a twofold cleavage, in which the cleavages are parallel with the lateral planes of the four-sided prism. The fragments are cubical. It sometimes occurs in thick and straight lamellar con cretions ; also large granular concretions. It alternates from transparent to strongly translucent, and refracts double. It is semi-hard ; it scratches calcareous-spar, but does not affect fluor-spar. It is brittle. It is very easily frangible. Specific gravity, 2.957, Bournon. 2.964, Klaproth. Chemical Characters. When exposed to the blowpipe, it does not exfoliate, and melt like gypsum, but becomes glazed over with a white friable enamel. Constituent Parts. According to Klaproth, it is a Sulphate of Lime, with out water, and with a slight admixture of Muriate of Soda. Gcognostic and Geographic Situations. It is sometimes met with in the gypsum of Notting hamshire *. In the salt-mines of Hall in the Tyrol; in those of Ilex in Switzerland; in quartz, along with talc, sulphur, and iron-pyritcs, in the mine of Pesay, also in Switzerland. Fifth * Grecnough.