Chalcopyrite [CuFeS2] is a copper iron sulfide that is often confused with the iron sulfide, pyrite [FeS2]. Both are sort of a brassy yellow color and tarnish (oxadise) upon exposure to oxygen. Chalcopyrite is much softer (3.5-4.0 Mohs) than pyrite (6.0-6.5). Pyrite (Isometric Crystal System) often occurs as cubes but sometimes as octahedrons and pyritohedrons. Chalcopyrite (Tetragonal Crystal System) crystals are often shaped like two wedges back-to-back (dispenoid). Both pyrite and chalcopyrite can have striated crystal faces and also occur as botryoidal masses. They also are found together but there is something about the color, tarnish and luster than distinguishes the two.
Our chalcopyrite specimens have been treated to accelerate the oxidisation process and give it the beautiful peacock hues.