Copper... [Cu]

Copper was first used by humans more than 10,000 years ago. A copper pendant discovered in what is now northern Iraq has been dated to about 8700 B.C.E. For nearly five millennia copper was the only metal known to humans. Early copper artifacts—first decorative, then utilitarian—were undoubtedly hammered out from "native copper," pure copper found in conjunction with copper-bearing ores in a few places around the world. By 5000 B.C.E., the dawn of metallurgy had arrived, as evidence exists of the smelting of simple copper oxide ores such as malachite and azurite.

Known worldwide copper resources are estimated at nearly 2.6 trillion kilograms (5.8 trillion pounds), of which only about 12 percent (300 billion kilograms; 804 billion pounds) has been mined throughout history. Nearly all of this mined copper is still in circulation, as copper's recycling rate is higher than that of any other engineering metal.

As a molten liquid, copper may be poured to form cake or slabs from which plate, sheet, strip, and foil are rolled; billet or logs from which tube, rod, bar, and forgings are extruded; wire rod from which wire is drawn; and ingot or bricks from which copper may be alloyed with other metals or used by foundries for casting.
There are more than 450 copper alloys, including brasses, bronzes, copper-nickels, nickel-silvers, and other specialty alloys. Copper is naturally a salmon color and may oxidize or patinate to gradually become dark brown or a greenish blue. Its alloys may range from pink to brown to gold to silver in color.
Copper is used extensively for its high thermal and electrical conductivity and corrosion resistance. In the United States, the most predominant of thousands of copper and copper alloy applications include building construction (largely sheet, tube, building wire, and hardware), 45 percent; electrical and electronic products, 26 percent; transportation equipment, 9 percent; industrial machinery and equipment, 10 percent; and consumer products, 10 percent.