Dioptase is a brightly colored mineral, highly desired for its intense green color. It can form in very distinctive, well-developed crystals, but only a handful of well-known deposits have produced large crystals. Dioptase is an extremely rare copper cyclosilicate mineral that crystallizes in small prismatic shards. This mineral occurs around other copper bearing minerals such as Chrysocolla, Malachite and Shattuckite. It forms on copper veins that have been exposed to extensive oxidation.