Native copper

Lore & Background

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

Reader's Guide

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 at this and many other locations, and evidence using isotopic analysis exists of copper trading routes throughout North America among native peoples. The first commercial mines in the Keweenaw Peninsula (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. A geological record of native copper being dragged by a glacier and deposited on the west branch of the Ontonagon River up river from Lake Superior is seen in the Ontonagon Boulder in the possession of the Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution. Another major native copper deposit is in Coro Coro, Bolivia.

Did You Know?

• Native copper is one of the few metallic elements to occur in native form.
• The largest deposits of native copper in the world are in the Keweenaw native copper deposits of Upper Michigan.
• Native Americans mined copper on a small scale at the Keweenaw and many other locations, with evidence of copper trading routes throughout North America.
• The Ontonagon Boulder, a record of native copper dragged by a glacier, is held by the Smithsonian Institution.