Thorianite
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
IMA symbolTho[1]
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 characteristics 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,[8] 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:[9]

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

Thorianite and uraninite form a complete solid solution series in synthetic and natural material.[10] 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%.[11] Rare earths, chiefly Ce, substitute for Th in amounts up to 8% by weight.[10][12] 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.[13]
  • Uranothorianite[14]
  • Thorianite Cerian[15][16]
  • Thorianite La bearing[15]

Occurrence

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

See also

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ↑ "Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2011-12-10.
  3. ↑ Mindat.org
  4. ↑ Webmineral data
  5. ↑ Frondel, C. (1958). Systematic Mineralogy of Uranium and Thorium. United States Government Printing Office.
  6. ↑ Coomaraswamy, A.K. (1904). "Uraninite". Spolia Zeylanica. Pt. 6 (2): 57.
  7. ↑ 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. S2CID 4032255.
  8. ↑ One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Thorianite". Encyclopædia Britannica. Vol. 26 (11th ed.). Cambridge University Press. p. 878.
  9. ↑ Kobayashi, M. (1912). "On the composition of thorianite". Tohoku Imp. Univ. Sci. Repts. 1 (Ist Ser): 201–206.
  10. 1 2 Palache, C.; H. Berman; C. Frondel (1944). Dana's System of Mineralogy, Volume 1. John Wiley and Sons, New York. pp. 620–622.
  11. ↑ Heinrich, E. W. (1958). Mineralogy and Geology of Radioactive Raw Materials. McGraw-Hill.
  12. ↑ Graham, A. R. (1955). "CERIANITE CeO2: A NEW RARE-EARTH OXIDE MINERAL". Am. Mineral. 40.
  13. ↑ Bespalov, M.M. (1941). "On discovery of a new mineral of the thorianite group [in Russian]". Sovietskaya Geologiya. II (6): 105–107.
  14. ↑ "Uranothorianite mineral information and data". Retrieved 2007-06-28.
  15. 1 2 "Minerals with crystal structure determined". Archived from the original on 2007-09-27. Retrieved 2007-06-27.
  16. ↑ "ICSD for WWW : Details (Thorianite Cerian)". Retrieved 2007-06-27.
  17. ↑ Viswanathan, P. (1953). "Thorianite in Travancore". Mineral. Mag. 88: 282.
  18. ↑ Lacroix, A. (1923). Minéralogie de Madagascar. Augustin Challamel, éditeur, Librairie maritime et coloniale.
  19. ↑ George, D'Arcy (1949). "Mineralogy of Uranium and Thorium Bearing Minerals". USAEC Technical Information Service, Oak Ridge, Tennessee. RMO-563: 198.
  20. ↑ White, M. G. (1952). Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska. GS-C-195, Geological Survey.
  21. ↑ 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}}: Cite journal requires |journal= (help)
  22. ↑ Lang, A. H.; J. W. Griffith; H. R. Steacy (1962). Canadian Deposits of Uranium and Thorium. Geological Survey of Canada.
  23. ↑ Robinson, S. C.; A. P. Sabina (1955). "Uraninite And Thorianite From Ontario And Quebec". Am. Mineral. 40.
  24. ↑ Hiemstra, S. A. (1955). "Baddeleyite from Phalaborwa, Eastern Transvaal". American Mineralogist. 40: 275–282.
  25. ↑ Ledoux, A. "Les roches cristallines du Kasai". Soc. Geol. Belgique Annales. 40: C177.
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