Tellurium

Tellurium is a brittle, silvery-white metalloid, with properties shared by metals and nonmetals. Although its crystals look metallic, tellurium is a semiconductor, and its electrical conductivity increases slightly in light. It is rare in Earth's crust, occurring both as the free element and in compounds with metals such as gold. Most commercial tellurium is recovered as a by-product of copper refining, from the material that collects as copper is purified using electricity. The compound cadmium telluride absorbs light in thin-film solar cells, helping turn sunlight into electricity. Small additions of tellurium also make copper alloys easier to cut and shape with machine tools.