A dark gray or black mineral, copper (I) sulfide
(Cu2S). Chalcocite is a major copper
ore found mainly in sulfur deposits. The
crystals occur in orthorhombic granular masses, or rarely in prismatic form.
It is found (often with bornite) in the
Ural Mountains, Africa, South America, Alaska, Connecticut, and the southern
United States. Hardness 2.5 to 3.0; relative density 5.7.
Image source: Mineralogical Information Institute
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