Thorianite



Thorianite
CategoryMineral
Chemical formulaThorium Oxide, ThO2
Identification
ColorDark gray, brown-black
Crystal habitRounded grains
Isometric
TwinningPenetration twins on {111} very common
CleavagePoor/Indistinct
FractureIrregular/Uneven,Sub-Conchoidal
Mohs Scale hardness6½ - 7
LusterResinous,Sub-Metallic
StreakGrey, Grey green to black
Density9.7 g/cm3
DiaphaneityTranslucent on thin edges

Thorianite is a rare mineral,[1] originally discovered by Ananda Coomaraswamy in 1904 as uraninite,[2] but recognized as a new species by W. R. Dunston.[3] It was so named on account of its high percentage of pitchblende but harder to shield due its high energy gamma rays. It is relatively more common in the alluvial gem-gravels of Sri Lanka, where it occurs mostly as water worn, small, heavy, black, cubic crystals. The largest crystals (sizes usually up to around 1.5 cm; very rare are sizes greater than 2.5 cm; largest is 6 cm and 2.2 kilos) came from Madagascar.

Chemistry

Based on color, specific gravity and composition three types of thorianite are distinguished:[4]

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

Thorianite and Rare earths, chiefly Ce, substitute for Th in amounts up to 8% by weight. [7][8] 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.[9]
  • Uranothorianite[10]
  • Thorianite Cerian[11][12]
  • Thorianite La bearing[11]

Occurrence

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

  • Sri Lanka - In stream gravels, Galle district, Southern Province; Balangonda district; near Kodrugala, S'abaragamuwa Province; and from a pegmatite in Bambarabotuwa area.
  • India - Reported from beach sands of Travancore (Kerala).[13]
  • Madagascar - Found in alluvial deposits of Betroka and Andolobe.[14] Also as very large crystals from Tôlanaro (Fort Dauphin); at Andranondambo and other localities.
  • Russia - In black sands of a gold placer on Boshogoch River, Transbaikalia, Siberia; in the Kovdor massif, 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;[15] black sands in Nixon Fork and Wiseman districts, Alaska.[16][17]
  • Canada - Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca;[18] Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.[19]
  • South Africa - Occurs with carbonatite at Phalaborwa, Eastern Transvaal.[20]
  • Belgian Congo[21]

See also

References

  1. ^ Frondel, C. (1958). Systematic Mineralogy of Uranium and Thorium. United States Government Printing Office. 
  2. ^ Coomaraswamy, A.K. (1904). "Uraninite". Spolia Zeylanica Pt. 6 (2): 57.
  3. ^ Dunston, W.R. (1904-03-31). "The occurrence of Thorium in Ceylon". Nature 69: 510-511.
  4. ^ Kobayashi, M. (1912). "On the composition of thorianite". Tohuku Imp. Univ. Sci. Repts. 1 (Ist Ser): 201-206.
  5. ^ Palache, C.; H. Berman, C. Frondel (1944). "Dana's System of Mineralogy". John Wiley and Sons, New York 1: 478–480.
  6. ^ Heinrich, E. W. (1958). Mineralogy and Geology of Radioactive Raw Materials. McGraw-Hill. 
  7. ^ Palache, C.; H. Berman, C. Frondel (1944). "Dana's System of Mineralogy". John Wiley and Sons, New York 1: 478–480.
  8. ^ Graham, A. R. (1955). "CERIANITE CeO2: A NEW RARE-EARTH OXIDE MINERAL". Am. Mineralogist 40.
  9. ^ Bespalov, M.M. (1941). "On discovery of a new mineral of the thorianite group [in Russian]". Sovietskaya Geologiya II (6): 105-107.
  10. ^ Uranothorianite mineral information and data. Retrieved on 2007-06-28.
  11. ^ a b Minerals with crystal structure determined. Retrieved on 2007-06-27.
  12. ^ ICSD for WWW : Details (Thorianite Cerian). Retrieved on 2007-06-27.
  13. ^ Viswanathan, P. (1953). "Thorianite in Travancore". Mineralog. Mag. 88: 282.
  14. ^ Lacroix, A. (1923). Minéralogie de Madagascar. Augustin Challamel, éditeur, Librairie maritime et coloniale. 
  15. ^ George, D'Arcy (1949). "Mineralogy of Uranium and Thorium Bearing Minerals". USAEC Technical Information Service, Oak Ridge, Tennessee: 198.
  16. ^ White, M. G. (1952). Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska. GS-C-195, Geological Survey. 
  17. ^ White, M. G.; J. M. Stevens (1953). "RECONNAISSANCE FOR RADIOACTIVE DEPOSITS IN THE RUBY-POORMAN DISTRICT, RUBY QUADRANGLE, CENTRAL ALASKA,1949". TEI-192, Geological Survey.
  18. ^ Lang, A. H.; J. W. Griffith, H. R. Steacy (1962). Canadian Deposits of Uranium and Thorium. Geological Survey of Canada. 
  19. ^ Robinson, S. C.; A. P. Sabina (1955). "URANINITE AND THORIANITE FROM ONTARIO AND QUEBEC". Am. Mineralogist 40.
  20. ^ Hiemstra, S. A. (1955). "Baddeleyite from Phalaborwa, Eastern Transvaal". American Mineralogist 40: 275-282.
  21. ^ Ledoux, A.. "Les roches cristallines du Kasai". Soc. Geol. Belgique Annales 40: C177.
  • This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
 
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