Copper - Encyclopedia

    Class : Elements
    Subclass : Metals
    Crystal system : Cubic
    Chemistry : Cu
    Rarity : Common

Copper, or native copper, is a secondary mineral typical of the oxidation and cementation zone of copper sulphide deposits, where it is associated with cuprite, azurite, malachite, chalcocite... More rarely, it is a primary mineral in certain basic lavas, associated with native silver and arsenides (Michigan deposit). It takes its name from the Latin cuprum, previously cyprium aes (Cyprus bronze), an island where this metal was mined in Antiquity. It rarely forms sharp crystals ; these are then cubic, dodecahedral, hexatetrahedral often deformed and reaching up to 15 cm. Copper is usually found in dendrites of small, flattened, twisted crystals, generally passing into filiform or arborescent aggregates ("fern leaves"), in "leaves", or in sometimes imposing dendritic masses (up to 420 tons in Michigan ). It commonly pseudomorph other copper minerals (oxides and sulfides) and sometimes even carbonates (aragonite). Like most metals, copper is very malleable. Bright pink in color with a bright metallic luster when it is fresh, it quickly tarnishes to red, turns to brown, then to black. The Michigan deposits were the only industrial holdings of native copper as copper ore, and were the world's largest source of this metal from 1850 until the 1920's. Currently copper is mainly extracted from sulphide (bornite, chalcopyrite, chalcocite) and oxides ( cuprite, tenorite), native copper only constituting a very secondary source of this metal. It can occasionally be cut into cabochon for jewelry.

In France, small clusters, sometimes spectacular, have been extracted from the Mine of St-Véran (Hautes-Alpes), that of Daluis (Alpes Maritime), as well as the fluorite mines of Albigeois (Le Burc, Le Moulinal, Montroc). Native copper is also naturally found on the Chessy copper mine (Rhône).

Copper twinning run on {111} (spinel twin law).

Some arborescent crystals can be glued on matrix. In addition to these assemblies, certain objects, whether mineral or organic, can be coated with copper by electrolysis and thus create false epigenies, this process is called electroplating. The ends of the covered body systematically present ball-shaped growths. Opposite, a scorpion treated with this process rather convincing because this specimen is presented in the showcase of an American museum...