Cobalt is a scarce, heavy, hard, lustrous, steel-gray metallic chemical element that is found in the earth's crust always in compounds except for small deposits contained in alloys with natural meteoric iron. It is also a constituent of tobacco smoke, because tobacco plants readily absorb it, along with other heavy metals, from the soil.
Cobalt is a trace element, and a component of vitamin B12, which is essential for all animals, and, in inorganic form, is also a micronutrient for bacteria, algae and fungi. However, it can be toxic to humans and other animals when swallowed, inhaled, or in prolonged contact with the skin and can accumulate in the liver, kidney, pancreas, heart, bones and muscles.
Cobalt compound pigments have been used since ancient times to give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. Cobalt's largest uses today are rechargeable lithium-ion batteries and magnetic, wear-resistant and high-strength alloys. An isotope, cobalt-60, is used as a radioactive tracer and for the production of high-energy gamma rays.
As with many other raw materials, there is also a much darker side to cobalt. The soaring demand, mainly for use in rechargeable battery electrodes, has led to severe human rights abuses and environmental damage in central Africa, and particularly in the Democratic Republic of Congo, the world’s largest producer of cobalt. The lack of safety precautions frequently causes injuries or death for the roughly 100,000 miners who dig mainly with hand tools, and the mining also pollutes the vicinity with toxic metals, affects indigenous communities and wildlife, and appears to cause birth defects and breathing difficulties.