te, 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.

_Metallurgy._--Copper is obtained from its ores by three principal
methods, which may be denominated--(1) the pyro-metallurgical or dry
method, (2) the hydro-metallurgical or wet method, and (3) the
electro-metallurgical method.