Uranium

Uranium is a dense, silvery metal and the heaviest element found in quantity in nature. Martin Heinrich Klaproth identified it in 1789 and named it after the newly discovered planet Uranus. In 1896, Henri Becquerel noticed uranium salts fogging photographic plates: the discovery of radioactivity. Today it is mined mostly in Kazakhstan, Canada and Australia.

Natural uranium is over 99% uranium-238, but the rare uranium-235, about 0.7%, can split and release enormous energy. Nuclear power plants run on uranium enriched to a few percent uranium-235. Leftover depleted uranium is used where great density helps, such as aircraft counterweights and armor. Glass containing a little uranium glows green under ultraviolet light.