What is chalcopyrite?
Chalcopyrite is copper iron sulphide, CuFeS2, and the most important copper-bearing sulphide mineral in many ore deposits. Its name and golden colour can invite comparison with pyrite, but chalcopyrite is softer, commonly more iridescent on alteration and has a different chemistry and crystal structure.
Mineralogy and structure
Chalcopyrite crystallises in the tetragonal system and belongs to the sulphides. It is opaque, metallic and has Mohs hardness about 3.5-4. Fresh surfaces are brass yellow, while the streak is dark greenish black. It is brittle and can show indistinct cleavage.
Colour and appearance
Fresh chalcopyrite is typically warm brass yellow with metallic lustre. Natural tarnish can produce blue, violet, green and red iridescence. Commercial material sold as “peacock ore” may be altered or deliberately treated to intensify colours, so its description should state observed condition rather than imply an untreated natural surface.
Formation and localities
Chalcopyrite is common in hydrothermal sulphide veins, porphyry copper deposits, volcanic massive sulphide deposits and disseminated mineralisation in igneous rocks. It occurs with pyrite, sphalerite, galena and quartz. Important collector localities include Romania, Cornwall in the UK, Peru, Mexico, Spain, the United States, Canada and South Africa.
Use in collections
Collectors value sharp crystals, bright unaltered faces and informative associations. Avoid damp storage and rough contact with other specimens: its attractive surface can tarnish and its hardness is modest for a metallic mineral.
