Chalcopyrite is an ore of copper with by products of gold and silver. In fact, 80 % of worlds copper comes from this ore. It usually forms brittle, metallic, compact masses with a brassy yellow, often tarnished or iridescent color, but is also found as striated tetragonal crystals. It's streak is greenish black and commonly occurs in igneous rocks as the original constituent from which many other copper minerals have been derived by alteration. It also occurs in pegmatites, contact metamorphic zones in limestone, and sulfide ore veins. It sometimes contains gold and silver as impurities.