Thorianite Explained

Boxbgcolor:	6d625d
Thorianite
Boxtextcolor:	fff
Category:	Oxide mineral
Formula:	Thorium oxide, ThO2
Imasymbol:	Tho^[1]
Strunz:	4.DL.05
System:	Isometric
Class:	Hexoctahedral (mm) H-M symbol: (4/m 2/m)
Symmetry:	Fm3m
Unit Cell:	a = 5.595 Å; Z = 4
Color:	Dark gray, brown-black
Habit:	Cubic crystals, usually rounded to some degree in detrital deposits
Twinning:	Penetration twins on common
Cleavage:	Poor/Indistinct
Fracture:	Irregular to uneven, sub-conchoidal
Mohs:	6.5 – 7
Luster:	Resinous, sub-metallic
Refractive:	n = 2.20 – 2.35
Opticalprop:	Isotropic
Streak:	Grey, grey green to black
Gravity:	9.7
Diaphaneity:	Opaque, translucent on thin edges
Other:	Radioactive
References:	^[2] ^[3] ^[4]

Thorianite is a rare thorium oxide mineral, ThO₂.^[5] It was originally described by Ananda Coomaraswamy in 1904 as uraninite,^[6] but recognized as a new species by Wyndham R. Dunstan.^[7] It was so named by Dunstan on account of its high percentage of thorium; it also contains the oxides of uranium, lanthanum, cerium, praseodymium and neodymium. Helium is present, and the mineral is slightly less radioactive than pitchblende, but is harder to shield due to its high energy gamma rays. It is common in the alluvial gem-gravels of Sri Lanka, where it occurs mostly as water worn, small, heavy, black, cubic crystals. The largest crystals are usually near 1.5 cm. Larger crystals, up to 6cm (02inches), have been reported from Madagascar.

Chemistry

Based on color, specific gravity and composition three types of thorianite are distinguished:^[8]

• α-thorianite
• β-thorianite
• γ-thorianite

Thorianite and uraninite form a complete solid solution series in synthetic and natural material.^[9] The division between the two species is at Th:U = 1:1 with U possibly making up to 46.50% and Th ranging up to 87.88%.^[10] Rare earths, chiefly Ce, substitute for Th in amounts up to 8% by weight.^{[9] [11]} Ce is probably present as Ce⁴⁺. Complete series is known in synthetic material between CeO₂ - PrO₂ - ThO₂ - UO₂. Small amounts of Fe³⁺ and Zr also may be isomorphous with Th. Pb present is probably radiogenic.

Varieties

• Aldanite – a variety of thorianite containing 14.9% to 29.0% UO₂ and 11.2% to 12.5% PbO.^[12]
• Uranothorianite^[13]
• Thorianite Cerian^{[14] [15]}
• Thorianite La bearing^[14]

Occurrence

Usually found in alluvial deposits, beach sands, heavy mineral placers, and pegmatites.

• Sri Lanka – In stream gravels, Galle district, Southern Province; Balangoda district; near Kodrugala, Sabaragamuwa Province; and from a pegmatite in Bambarabotuwa area.
• India – Reported from beach sands of Travancore (Kerala).^[16]
• Madagascar – Found in alluvial deposits of Betroka and Andolobe.^[17] Also as very large crystals from Fort Dauphin; at Andranondambo and other localities.
• Russia – In black sands of a gold placer on Boshogoch River, Transbaikalia, Siberia; in the Kovdor Massif by Kovdor, Kola Peninsula; in the Yenisei Range, Siberia.
• United States – reported from Easton, Pennsylvania; black sands in Missouri River, near Helena, Montana; Scott River, Siskiyou County, California;^[18] black sands in Nixon Fork and Wiseman districts, Alaska.^{[19] [20]}
• Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca;^[21] Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.^[22]
• South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal.^[23]
• Democratic Republic of Congo - Kasaï region^[24]

See also

• Uraninite
• Thorite
• Classification of minerals
• List of minerals

External links

• Uraniumminerals.com
• Mindat.org

Notes and References

1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3. 291–320. 10.1180/mgm.2021.43. 2021MinM...85..291W. 235729616. free.
2. Web site: Handbook of Mineralogy . 2011-12-10 . 2016-03-03 . https://web.archive.org/web/20160303170830/http://www.handbookofmineralogy.com/pdfs/thorianite.pdf . dead .
3. http://www.mindat.org/min-3944.html Mindat.org
4. http://www.webmineral.com/data/Thorianite.shtml Webmineral data
5. Book: Frondel , C. . United States Government Printing Office. Systematic Mineralogy of Uranium and Thorium. 1958.
6. Pt. 6. 2. 57. Coomaraswamy. A.K.. Uraninite. Spolia Zeylanica. 1904.
7. 69. 510–511. Dunstan. Wyndham R.. The occurrence of Thorium in Ceylon. Nature. 1904-03-31. 10.1038/069510d0. 1796. 1904Natur..69..510D . 4032255.
8. 1. Ist Ser. 201–206. Kobayashi. M.. On the composition of thorianite. Tohoku Imp. Univ. Sci. Repts.. 1912.
9. Book: Palache , C. . 620–622. H. Berman . C. Frondel . Dana's System of Mineralogy, Volume 1. John Wiley and Sons, New York. 1944.
10. Book: Heinrich , E. W. . McGraw-Hill. Mineralogy and Geology of Radioactive Raw Materials. 1958.
11. 40. Graham. A. R.. CERIANITE CeO₂: A NEW RARE-EARTH OXIDE MINERAL. Am. Mineral.. 1955.
12. II. 6. 105–107. Bespalov. M.M.. On discovery of a new mineral of the thorianite group [in Russian]. Sovietskaya Geologiya. 1941.
13. Web site: Uranothorianite mineral information and data. 2007-06-28.
14. Web site: Minerals with crystal structure determined . 2007-06-27 . dead . https://web.archive.org/web/20070927022021/http://sdpd.univ-lemans.fr/minknown.html#T . 2007-09-27.
15. Web site: ICSD for WWW : Details (Thorianite Cerian) . 2007-06-27 .
16. 88. 282. Viswanathan. P.. Thorianite in Travancore. Mineral. Mag.. 1953.
17. Book: Lacroix , A. . Augustin Challamel, éditeur, Librairie maritime et coloniale. Minéralogie de Madagascar. 1923.
18. 198. George. D'Arcy. Mineralogy of Uranium and Thorium Bearing Minerals. USAEC Technical Information Service, Oak Ridge, Tennessee. RMO-563. 1949.
19. Book: White , M. G. . GS-C-195, Geological Survey. Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska. 1952.
20. TEI-192, Geological Survey. White. M. G.. J. M. Stevens . Reconnaissance For Radioactive Deposits In The Ruby-Poorman District, Ruby Quadrangle, Central Alaska,1949. 1953.
21. Book: Lang , A. H. . Geological Survey of Canada. J. W. Griffith . H. R. Steacy . Canadian Deposits of Uranium and Thorium. 1962.
22. 40. Robinson. S. C.. A. P. Sabina . Uraninite And Thorianite From Ontario And Quebec. Am. Mineral.. 1955.
23. 40. 275–282. Hiemstra. S. A.. Baddeleyite from Phalaborwa, Eastern Transvaal. American Mineralogist. 1955.
24. 40. C177. Ledoux. A.. Les roches cristallines du Kasai . Soc. Geol. Belgique Annales.