Native copper

Native copper (specimen ~4 cm)

Copper, as native copper, is one of the few metallic elements to occur in uncombined form as a natural mineral, although most commonly occurs in oxidized states and mixed with other elements. Native copper was an important ore of copper in historic times and was used by pre-historic peoples.

Native copper occurs as rarely isometric cubic and octahedral crystals, but more typically as irregular masses and fracture fillings. It has a reddish, orangish, and/or brownish color on fresh surfaces, but typically is weathered and coated with a green tarnish of copper(II) carbonate (also known as patina or verdigris). Its specific gravity is 8.9 and its hardness is 2.5-3.

The mines of the Keweenaw native copper deposits of Upper Michigan were major copper producers in the 19th and early 20th centuries, and are the largest deposits of native copper in the world. Native Americans mined copper on a small scale, and evidence exists of copper trading routes throughout North America among native peoples, proven by isotopic analysis. The first commercial mines in the Keweenaw Peninsula (which is nicknamed the "Copper Country" and "Copper Island)", opened in the 1840s. Isle Royale in western Lake Superior was also a site of many tons of native copper. Some of it was extracted by native peoples, but only one of several commercial attempts at mining turned a profit there.

Another major native copper deposit is in Corocoro, Bolivia.

The name copper comes from the Greek kyprios, of Cyprus, the location of copper mines since pre-historic times.

Further reading

• Thurner, Arthur W. Strangers and Sojourners – A History of Michigan's Keweenaw Peninsula; Wayne State University Press: Detroit, 1994. ISBN 0814323960.
• Prehistoric Copper in Wisconsin; Mississippi Valley Archaeology Center, <http://www.uwlax.edu/mvac/PreEuropeanPeople/EarlyCultures/native_nativecopper.html>. (accessed 26 June 2005).