Float Copper

A mass of native copper weighing 9,392 pounds was found in 1970 buried under three feet of soil, or glacial till, about 4½ miles southwest of Calumet. Float copper like this was torn loose from fissures and lodes by glacial action and, with other rock materials, carried by the ice sheet for great distances before being deposited as glacial debris or till. Churning and grinding at the base of the glacier rounded and smoothed the copper mass, producing its lobate form. Its long burial of about 9,000 years since the end of glacial action accounts for the thorough oxidation of its surface. The oxidation products are primarily malachite, a green copper carbonate, and cuprite, a red copper oxide. Similar pieces were often discovered in Keweenaw and on Isle Royale.

Michigan · United States