Covellite (aka covelline) is a crystalline form of copper sulfide (CuS). In appearance it is a deep metallic indigo blue (tarnished to purple or black) with iridescent yellow and red flashes. It is associated with chalcosite in zones of secondary enrichment (supergene) of copper sulfide deposits. Commonly found with and as coatings on chalcocite, chalcopyrite, bornite, enargite, pyrite, and other sulfides. Often occurs as pseudomorphic replacements after other minerals. Very rare occurrence as a volcanic sublimate at Mount Vesuvius the site of its discovery or first description by N. Covelli (1790 - 1829).
All the covellite I work with is from Butte, Montana USA. It has also been found in other parts of the world Germany; Austria and South America to name a few.