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sulfosalt mineral, copper arsenic sulfide (Cu3AsS4), that is occasionally an important ore of copper. It occurs as heavy, metallic-gray crystals and masses in veins and replacement deposits. Economically valuable deposits have been found in the Balkans; at several places in Peru; Chuquicamata, Chile; and Butte, Mont. It forms orthorhombic crystals. For detailed physical properties, see sulfosalt (table)