Never found as crystals, it is green or bluish-green in color, and often has the appearance of opal or enamel, being translucent and having a conchoidal fracture with vitreous luster; sometimes it is earthy in texture. Not being a definite crystallized substance, it varies widely in chemical composition, hardness and specific gravity. Various impurities (silica, &c.) are also commonly present, and several varieties have been distinguished by special names. The mineral occurs in the upper parts of veins of copper ores, and has resulted from their alteration by the action of waters containing silica in solution. Pseudomorphs of chrysocolla after various copper minerals (e.g. cuprite) are not uncommon. It is found in most copper mines.*