Thorianite

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Thorianite
Thorianite-54888.jpg
Group of interpenetrating twinned thorianite crystals from Ambatofotsy, Madagascar (size: 1.6 x 1.4 x 1.3 cm)
General
CategoryOxide mineral
Formula
(repeating unit)		Thorium oxide, ThO2
Strunz classification4.DL.05
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupFm3m
Unit cella = 5.595 Å; Z = 4
Identification
ColorDark gray, brown-black
Crystal habitCubic crystals, usually rounded to some degree in detrital deposits
TwinningPenetration twins on {111} common
CleavagePoor/Indistinct
FractureIrregular to uneven, sub-conchoidal
Mohs scale hardness6.5 – 7
LusterResinous, sub-metallic
StreakGrey, grey green to black
DiaphaneityOpaque, translucent on thin edges
Specific gravity9.7
Optical propertiesIsotropic
Refractive indexn = 2.20 – 2.35
Other characteristicsRadioactive.svg Radioactive
References[1][2][3]

Thorianite is a rare thorium oxide mineral, ThO2.[4] It was originally described by Ananda Coomaraswamy in 1904 as uraninite,[5] but recognized as a new species by Wyndham R. Dunstan.[6] 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,[7] 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 6 cm (2.4 in), 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.

See also[]

References[]

  1. ^ Handbook of Mineralogy
  2. ^ Mindat.org
  3. ^ Webmineral data
  4. ^ Frondel, C. (1958). Systematic Mineralogy of Uranium and Thorium. United States Government Printing Office.
  5. ^ Coomaraswamy, A.K. (1904). "Uraninite". Spolia Zeylanica. Pt. 6 (2): 57.
  6. ^ Dunstan, Wyndham R. (1904-03-31). "The occurrence of Thorium in Ceylon". Nature. 69 (1796): 510–511. Bibcode:1904Natur..69..510D. doi:10.1038/069510d0.
  7. ^  One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Thorianite". Encyclopædia Britannica. 26 (11th ed.). Cambridge University Press. p. 878.
  8. ^ Kobayashi, M. (1912). "On the composition of thorianite". Tohoku Imp. Univ. Sci. Repts. 1 (Ist Ser): 201–206.
  9. ^ a b Palache, C.; H. Berman; C. Frondel (1944). Dana's System of Mineralogy, Volume 1. John Wiley and Sons, New York. pp. 620–622.
  10. ^ Heinrich, E. W. (1958). Mineralogy and Geology of Radioactive Raw Materials. McGraw-Hill.
  11. ^ Graham, A. R. (1955). "CERIANITE CeO2: A NEW RARE-EARTH OXIDE MINERAL". Am. Mineral. 40.
  12. ^ Bespalov, M.M. (1941). "On discovery of a new mineral of the thorianite group [in Russian]". Sovietskaya Geologiya. II (6): 105–107.
  13. ^ "Uranothorianite mineral information and data". Retrieved 2007-06-28.
  14. ^ a b "Minerals with crystal structure determined". Archived from the original on 2007-09-27. Retrieved 2007-06-27.
  15. ^ "ICSD for WWW : Details (Thorianite Cerian)". Retrieved 2007-06-27.[permanent dead link]
  16. ^ Viswanathan, P. (1953). "Thorianite in Travancore". Mineral. Mag. 88: 282.
  17. ^ Lacroix, A. (1923). Minéralogie de Madagascar. Augustin Challamel, éditeur, Librairie maritime et coloniale.
  18. ^ George, D'Arcy (1949). "Mineralogy of Uranium and Thorium Bearing Minerals". USAEC Technical Information Service, Oak Ridge, Tennessee. RMO-563: 198.
  19. ^ White, M. G. (1952). Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska. GS-C-195, Geological Survey.
  20. ^ 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. Cite journal requires |journal= (help)
  21. ^ Lang, A. H.; J. W. Griffith; H. R. Steacy (1962). Canadian Deposits of Uranium and Thorium. Geological Survey of Canada.
  22. ^ Robinson, S. C.; A. P. Sabina (1955). "Uraninite And Thorianite From Ontario And Quebec". Am. Mineral. 40.
  23. ^ Hiemstra, S. A. (1955). "Baddeleyite from Phalaborwa, Eastern Transvaal". American Mineralogist. 40: 275–282.
  24. ^ Ledoux, A. "Les roches cristallines du Kasai". Soc. Geol. Belgique Annales. 40: C177.

External links[]

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