Copper, one of the first metals to be used by humans, has an atomic number of 29 and an atomic weight of 63.546. In its solid state, copper (atomic symbol: Cu) is extremely ductile and durable; it withstands temperature changes without breaking and is an excellent thermal and electrical conductor. Copper melts at 1983.7°F (1084.6°C), is nonmagnetic, and exhibits low chemical activity. The word copper was derived from cuprum, the Latin term for Cyprus, where most of the Roman supply of copper was mined.
Native copper--pure copper found in nature--was once abundant in the United States; the largest known deposits of native copper were found in the Keweenaw Peninsula of northern Michigan. Now most copper is refined from such ores as chalcocite, chalcopyrite, bornite, cuprite, malachite, and azurite, and it is mined primarily in Chile, the United States, Indonesia, Peru, and Australia. (As of 2006, Chile leads the world in both mining production and copper reserves.) The metal is extracted by smelting, or by a combination of leaching and electrolysis.
Copper is used in its pure state, in alloys, and in chemical compounds for a wide range of applications. Pure copper is used extensively for electrical wiring because of its excellent electrical conductivity. The pure metal is also useful for plumbing and natural gas fittings in buildings; copper's malleability and resistance to corrosion make copper pipes easy to install and maintain. Pure copper is also used in such applications as kitchen utensils and automotive radiator cores, where temperature changes would cause other metals to crack or become deformed.
Three classes of commercially important alloys are made by melting copper together with other metals to add strength and tarnish resistance, or to make metals more suitable for casting and machining than pure copper. Bronzes are composed of copper and tin; brasses contain copper and zinc; and nickel silvers are made with copper, nickel, and zinc. These alloys are used for thousands of applications, from machinery parts to costume jewelry. Such copper compounds as blue vitriol, cuprous cyanide, and Paris green are also used for numerous applications (including agricultural pesticides, pigments and mordants in dyeing, and electroplating solutions). From the beginning of the Iron Age (around 1000 BC), copper remained the second most important metal in human use until the 1960s, when it was superseded in world production by cheaper, lighter, more plentiful aluminum.