Chalcopyrite, copper iron sulfide, is one of the most widespread and important ores of copper. It occurs both as disseminated grains in a host rock, and also in vein-type deposits along with pyrite, galena, sphalerite and other sulfide minerals. Chalcopyrite has a golden yellow color, but the surface tarnishes rapidly upon exposure to air leaving a characteristic brightly colored iridescent film. The material from Butte, Montana shows off this property very well.