Chalcopyrite (KAL-co-PIE-rite) usually occurs in massive form, like this specimen, rather than in crystals, but its crystals are unusual among the sulfides in having a shape like a four-sided pyramid (technically they are scalenohedra). It has a Mohs hardness of 3.5 to 4, a metallic luster, a greenish black streak and a golden color that is commonly tarnished in various hues (though not the brilliant blue of bornite). Chalcopyrite is softer and yellower than pyrite, more brittle than gold. It is often mixed with pyrite.
Chalcopyrite may have various amounts of silver in place of the copper, gallium or indium in place of the iron, and selenium in place of the sulfur. Thus these metals are all byproducts of copper production.