chalcopyrite or copper pyrites, brass-yellow mineral, sometimes with an iridescent tarnish. It is a sulfide of copper and iron, CuFeS₂ . It crystallizes in the tetragonal system but is usually found in the massive form. Chalcopyrite is of primary origin and occurs in igneous and metamorphic rocks and in metalliferous veins. It is an important ore of copper and is widely distributed throughout the world.