Uraninite used to be known as pitchblende (from
pitch, because of its black color, and
blende, from
blenden meaning "to deceive", 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 or not economically feasible). The mineral has been known since at least 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. All uraninite minerals contain a small amount of
radium as a
radioactive decay product of uranium.
Marie Skłodowska-Curie used pitchblende, processing tons of it herself, as the source material for her isolation of pure metallic radium in 1910. Uraninite also always contains small amounts of the
lead isotopes 206Pb and 207Pb, the end products of the decay series of the uranium isotopes 238U and 235U respectively. Small amounts of
helium are also present in uraninite as a result of
alpha decay. Helium was first found on Earth in
cleveite, an impure radioactive variety of uraninite, after having been discovered
spectroscopically in the
Sun's atmosphere. The extremely rare elements
technetium and
promethium can be found in uraninite in very small quantities (about 200
pg/kg and 4
fg/kg respectively), produced by the
spontaneous fission of
uranium-238. Francium can also be found in uraninite at 1
francium atom for every 1 × 1018 uranium atoms in the
ore as a result from the decay of
actinium. ==Occurrence==