Copper

Among the first metals worked by humans, native copper appears in artifacts dating back more than ten thousand years. It is a native element with a copper-red color that tarnishes to brown or green, crystallizing in the cubic system and forming dendritic, massive, or wire-like habits. The metal shows a metallic luster, a copper-red streak, no cleavage, and a hackly fracture; its Mohs hardness is 2.5 to 3 and its specific gravity 8.90. Native copper occurs in basaltic lava flows and sandstone deposits, and the Keweenaw Peninsula in Michigan yielded enormous masses of the pure metal. Its softness, malleability, and hackly fracture reflect the ductile behavior typical of the native metals.

Native copper was one of the first metals used by humans, with artifacts dating back over 10,000 years. It occurs in basaltic lava flows and sandstone deposits. The Keweenaw Peninsula in Michigan produced enormous masses of native copper.