Uraninite

Uraninite
Pitchblende from Niederschlema-Alberoda deposit, Germany
General
Category	Oxide minerals
Formula (repeating unit)	Uranium dioxide or uranium(IV) oxide (UO2)
Strunz classification	4.DL.05
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fm3m
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.
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, formerly pitchblende, 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. Marie Curie used pitchblende, processing tons of it herself, as the source material for her isolation of radium in 1898.