1911 Encyclopædia Britannica/Covellite

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COVELLITE, a mineral species consisting of cupric sulphide, CuS, crystallizing in the hexagonal system. It is of less frequent occurrence in nature than copper-glance, the orthorhombic cuprous sulphide. Crystals are very rare, the mineral being usually found as compact and earthy masses or as a blue coating on other copper sulphides. Hardness 1½-2; specific gravity 4.6. The dark indigo-blue colour is a characteristic feature, and the mineral was early known as indigo-copper (Ger. Kupferindig). The name covellite is taken from N. Covelli, who in 1839 observed crystals of cupric sulphide encrusting Vesuvian lava, the mineral having been formed here by the interaction of hydrogen sulphide and cupric chloride, both of which are volatile volcanic products. Covellite is, however, more commonly found in copper-bearing veins, where it has resulted by the alteration of other copper sulphides, namely chalcopyrite, copper-glance and erubescite. It is found in many copper mines; localities which may be specially mentioned are Sangerhausen in Prussian Saxony, Butte in Montana, and Chile; in the Medicine Bow Mountains of Wyoming a platiniferous covellite is mined, the platinum being present as sperrylite (platinum arsenide). (L. J. S.)