Pitchblende is a radioactive, uranium-rich mineral and ore. It has a chemical composition that is largely UO, but also contains UO and oxides of lead, thorium, and rare earth elements. It is known as pitchblende due to its black color and high density. It is also commonly referred to as Uraninite. The mineral has been known at least since the 15th century from silver mines in the Ore Mountains, on the German/Czech border. Pitchblende found in Germany was used by M. Klaproth in 1789 to discover the element uranium.