| Uraninite | |
|---|---|
 Pitchblende from Niederschlema-Alberoda deposit,Germany | |
| General | |
| Category | Oxide minerals |
| Formula | Uranium dioxide oruranium(IV) oxide (UO2) |
| IMA symbol | Urn[1] |
| Strunz classification | 4.DL.05 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m3 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 and green-gray (thin fragments) |
| 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 |  Radioactive 70Bq/g to 150 kBq/g |
| References | [2][3][4][5] |
| Major varieties | |
| Pitchblende | Massive |
Uraninite, also known aspitchblende, is aradioactive,uranium-richmineral andore with achemical composition that is largelyUO2 but because ofoxidation typically contains variable proportions ofU3O8.Radioactive decay of the uranium causes the mineral to containoxides oflead and trace amounts ofhelium. It may also containthorium andrare-earth elements.[2][4]
Uraninite used to be known as pitchblende (frompitch, because of its black color, andblende, fromblenden 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 theOre Mountains, on the German/Czech border. Thetype locality is the historic mining and spa town known as Joachimsthal, the modern-dayJáchymov, on theCzech side of the mountains, where F. E. Brückmann described the mineral in 1772.[4][6] Pitchblende from theJohanngeorgenstadt deposit in Germany was used byM. Klaproth in 1789 to discover the elementuranium.[7]
All uraninite minerals contain a small amount ofradium as aradioactive decay product of uranium.Marie Curie used pitchblende, processing tons of it herself, as the source material for her isolation of pure metallic radium in 1910.[8]
Uraninite also always contains small amounts of thelead isotopes206Pb and207Pb, the end products of the decay series of the uranium isotopes238U and235U respectively. Small amounts ofhelium are also present in uraninite as a result ofalpha decay. Helium was first found on Earth incleveite, an impure radioactive variety of uraninite, after having been discoveredspectroscopically in theSun's atmosphere. The extremely rare elementstechnetium andpromethium can be found in uraninite in very small quantities (about 200 pg/kg and 4 fg/kg respectively), produced by thespontaneous fission ofuranium-238. Francium can also be found in uraninite at 1francium atom for every 1 × 1018 uranium atoms in theore as a result from the decay ofactinium.
Uraninite is a major ore of uranium. Some of the highest-grade uranium ores in the world were found in theShinkolobwe mine in theDemocratic Republic of the Congo (the initial source for theManhattan Project) and in theAthabasca Basin in northernSaskatchewan, Canada. Another important source of pitchblende is atGreat Bear Lake in theNorthwest Territories of Canada, where it is found in large quantities associated withsilver. It also occurs inAustralia, theCzech Republic,Germany,England,Rwanda,Namibia andSouth Africa. In the United States, it can be found in the states ofArizona,Colorado,Connecticut,Maine,New Hampshire,New Mexico,North Carolina andWyoming. The geologistCharles Steen made a fortune on the production of uraninite in his Mi Vida mine inMoab, Utah. Uranium ores from theOre Mountains (today the border between the Czech Republic and Germany) were an important supply of both the wartimeGerman nuclear program (which failed to produce a bomb) and theSoviet nuclear program. Mining for uranium in the Ore Mountains (under the auspices ofSDAG Wismut after the war) ceased after the collapse of theGerman Democratic Republic.
Uranium ore is generally processed close to the mine intoyellowcake, which is an intermediate step in the processing of uranium.
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