"native," or elemental copper can be found in nature, but most copper is mined as oxide or sulfide minerals. Chalcopyrite (cufes2) is one copper mineral that can be converted to elemental copper in a series of chemical steps. Reacting chalcopyrite with oxygen at high temperature produces a mixture of copper sulfide and iron oxide. The iron oxide is separated from cus by reaction with sand (sio2). Cus is converted to cu2s in the process and the cu2s is burned in air to produce cu and so2:.