Uraninite

"Pitchblende" redirects here. For other uses, see Pitchblende (disambiguation).

Uraninite
Pitchblende from Niederschlema-Alberoda deposit, Germany
General
Category	Oxide minerals
Formula (repeating unit)	Uranium dioxide or uranium(IV) oxide (UO2)
Strunz classification	04.DL.05
Crystal symmetry	Isometric, hexoctahedral H-M symbol: (4/m32/m) Space group: F m3m
Unit cell	a = 5.4682 Å; Z = 4
Identification
Color	Steel-black to velvet-black, brownish black, pale gray to pale green; in transmitted light, pale green, pale yellow to deep brown
Crystal habit	Massive, botryoidal, granular. Octahedral crystals uncommon.
Crystal system	Isometric
Cleavage	Indistinct
Fracture	Conchoidal to uneven
Mohs scale hardness	5–6
Luster	Submetallic, greasy, dull
Streak	Brownish black, gray, olive-green
Diaphaneity	Opaque; transparent in thin fragments
Specific gravity	10.63–10.95; decreases on oxidation
Optical properties	Isotropic
Other characteristics	Radioactivity: 70 Bq/g to 150 kBq/g
References
Major varieties
Pitchblende	Massive

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 U₃O₈. 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.

All uraninite minerals contain a small amount of radium as a radioactive decay product of uranium. 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 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.

Occurrence

Uraninite crystals from Topsham, Maine (size: 2.7×2.4×1.4 cm)

Uraninite is a major ore of uranium. Some of the highest grade uranium ores in the world were found in the Shinkolobwe mine in the Democratic Republic of the Congo (the initial source for the Manhattan Project) and in the Athabasca Basin in northern Saskatchewan, Canada. Another important source of pitchblende is at Great Bear Lake in the Northwest Territories of Canada, where it is found in large quantities associated with silver. It also occurs in Australia, the Czech Republic, Germany, England, Rwanda and South Africa. In the United States it can be found in the states of Arizona, Colorado, Connecticut, Maine, New Hampshire, New Mexico, North Carolina and Wyoming. The geologist Charles Steen made a fortune on the production of Uraninite in his Mi Vida mine in Moab, Utah.

Uranium ore is generally processed close to the mine into yellowcake, which is an intermediate step in the processing of uranium.

See also

• Thorianite
• Uranium ore deposits
• List of minerals
• List of uranium mines

External links

Media related to at Wikimedia Commons