Uraninite is a
radioactive, uranium-rich
mineral and
ore with a
chemical composition that is largely
UO2, but due to
oxidation the mineral typically contains variable proportions of U
3O
8. Additionally, due to
radioactive decay, the ore also contains
oxides of
lead and trace amounts of
helium. It may also contain
thorium, and
rare earth elements. It used to be known as
pitchblende (from
pitch, because of its black color, and
blende, a term used by German miners to denote minerals whose density suggested metal content, but whose exploitation, at the time they were named, was either unknown, impossible or not economically feasible). The mineral has been known at least since the 15th century from silver mines in the
Ore Mountains, on the German/Czech border. The
type locality is the historic mining and spa town known as Joachimsthal, the modern day
Jáchymov, on the
Czech side of the mountains, where F.E. Brückmann described the mineral in 1772. Pitchblende from the
Johanngeorgenstadt deposit in Germany was used by
M. Klaproth in 1789 to discover the element
uranium.