342 METALLIC SALTS. 1. Oblique double four-sided pyramid. 2. Ilhomb, variously modified by truncations on the angles and edges. 3. Capillary crystals. It is shining, both externally and internally, and the lustre is vitreous, with exception of the capillary varie ties, which are pearly. 1 he fracture is flat conchoidal or foliated, and occa sionally fibrous. It alternates from semi-transparent to opaque. It refracts double. It is soft. It is friable, brittle, and easily frangible. Specific gravity, 1.972, Brinson. It tastes sweetish, styptic, and metallic. Chemical Characters. Before the blowpipe, on charcoal, it becomes magnetic, and colours glass of borax green. Constituent Parts. Oxide of Iron, - . 2,5.7 Sulphuric Acid, - . 2H.9 Water, ... 454 100.0 Berzelius. Geognostic and. Geographic Situations. It is always associated with iron-pyrites, by the decom- position-of which it is formed. It occurs in several coal mines in this country, and in many iron and coal mines on the Continent of Europe ; and also in America, and Asia. v Uses.
