_Ores._--The principal ores of copper are the oxides cuprite and melaconite, the carbonates malachite and chessylite, the basic chloride atacamite, the silicate chrysocolla, the sulphides chalcocite, chalcopyrite, erubescite and tetrahedrite. Cuprite (q.v.) occurs in most cupriferous mines, but never by itself in large quantities. Melaconite (q.v.) was formerly largely worked in the Lake Superior region, and is abundant in some of the mines of Tennessee and the Mississippi valley. Malachite is a valuable ore containing about 56% of the metal; it is obtained in very large quantities from South Australia, Siberia and other localities. Frequently intermixed with the green malachite is the blue carbonate chessylite or azurite (q.v.), an ore containing when pure 55.16% of the metal. Atacamite (q.v.) occurs chiefly in Chile and Peru. Chrysocolla (q.v.) contains in the pure state 30% of the metal; it is an abundant ore in Chile, Wisconsin and Missouri. The sulphur compounds of copper are, however, the most valuable from the economic point of view. Chalcocite, redruthite, copper-glance (q.v.) or vitreous copper (Cu2S) contains about 80% of copper. Copper pyrites, or chalcopyrite, contains 34.6% of copper when pure; but many of the ores, such as those worked specially by wet processes on account of the presence of a large proportion of iron sulphide, contain less than 5% of copper. Cornish ores are almost entirely pyritic; and indeed it is from such ores that by far the largest proportion of copper is extracted throughout the world. In Cornwall copper lodes usually run east and west. They occur both in the "killas" or clay-slate, and in the "growan" or granite. Erubescite (q.v.), bornite, or horseflesh ore is much richer in copper than the ordinary pyrites, and contains 56 or 57% of copper. Tetrahedrite (q.v.), fahlerz, or grey copper, contains from 30 to 48% of copper, with arsenic, antimony, iron and sometimes zinc, silver or mercury. Other copper minerals are percylite (PbCuCl2(OH)2), boleite (3PbCuCl2(OH)2, AgCl), stromeyerite { (Cu, Ag)2S}, cubanite (CuS, Fe2S3), stannite (Cu2S, FeSnS3), tennantite (3Cu2S, As2S3), emplectite (Cu2S, Bi2S3), wolfsbergite (Cu2S, Sb2S3), famatinite (3Cu2S, Sb2S5) and enargite (3Cu2S, As2S5). For other minerals, see COMPOUNDS OF COPPER below.