melanterite

[Lat. melanteria of Pliny; Gr. melantéria a black metallic dye, ink; Fr. melantérie.] Min.: A monoclinic salt originating in the decomposition of marcasite or pyrites (q. v.) by exposure to the atmosphere and moisture. Rarely crystallized, except artificially, but occurs in fibrous, stalactitic, and stalagmitic forms. Hardne , 2; specific gravity, 1832; luster, vitreous; color, various shades of green; taste, astringent and metallic. Brittle. Soluble in water. Composition: Sulphuric acid, 28:8; protoxide of iron, 25.9; water, 45-3-100. Formula, FeOSO3+HO. Used in dye ing, tanning, and the making of ink and Pru ian blue.