Occurrence
Native copper from the Keweenaw Peninsula Michigan about 2.5 inches (6.4 cm) long
Copper is synthesized in massive stars[18] and is present in the Earth's crust at a concentration of about 50 parts per million (ppm),[19] where it occurs as native copper or in minerals such as the copper sulfides chalcopyrite and chalcocite, the copper carbonates azurite and malachite, and the copper(I) oxide mineral cuprite.[9] The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US.[19] Native copper is a polycrystal, with the largest described single crystal measuring 4.4×3.2×3.2 cm.