chalcopyrite, the most common copper mineral, a copper and iron sulfide, and a very important copper ore. It typically occurs in ore veins deposited at medium and high temperatures, as in Río Tinto, Spain; Ani, Japan; Butte, Mont.; and Joplin, Mo. Chalcopyrite (Cu2Fe2S4) is a member of a group of sulfide minerals that crystallize in the tetragonal system; the group also includes stannite. Both minerals have crystalline structures related to sphalerite. For detailed physical properties, see sulfide mineral (table).