ARGENTITE

a silver sulfide mineral (Ag2S) that is the most important ore of silver. It is abundant, with other silver minerals, in the sulfide mineral deposits of Kongsberg, Nor.; Kremnica, Slovakia; Zacatecas, Mex.; and the Comstock Lode, Nev., U.S. Argentite, like several other sulfides, selenides, and tellurides of silver and copper, forms isometric crystals at high temperatures, but upon cooling the crystals invert from isometric (cubic) to nonisometric structures while remaining unchanged in external appearance. For example, argentite gives an X-ray pattern identical to that of acanthite, its orthorhombic modification (stable below 91 C, or 196 F). This shows that despite its isometric appearance argentite consists of lamellae of orthorhombic crystals, formed after the overall crystal shape was determined. For detailed physical properties, see sulfide mineral (table).