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.
| Thorianite | |
|---|---|
 Group of interpenetrating twinned thorianite crystals from Ambatofotsy, Madagascar (size: 1.6 x 1.4 x 1.3 cm) | |
| General | |
| Category | Oxide mineral |
| Formula (repeating unit) | Thorium oxide, ThO2 |
| IMA symbol | Tho[1] |
| Strunz classification | 4.DL.05 |
| Crystal system | Isometric |
| Crystal class | Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m) |
| Space group | Fm3m |
| Unit cell | a = 5.595 Å; Z = 4 |
| Identification | |
| Color | Dark gray, brown-black |
| Crystal habit | Cubic crystals, usually rounded to some degree in detrital deposits |
| Twinning | Penetration twins on {111} common |
| Cleavage | Poor/Indistinct |
| Fracture | Irregular to uneven, sub-conchoidal |
| Mohs scale hardness | 6.5 – 7 |
| Luster | Resinous, sub-metallic |
| Streak | Grey, grey green to black |
| Diaphaneity | Opaque, translucent on thin edges |
| Specific gravity | 9.7 |
| Optical properties | Isotropic |
| Refractive index | n = 2.20 – 2.35 |
| Other characteristics |  Radioactive |
| References | [2][3][4] |
Chemistry
editBased 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
editOccurrence
editUsually 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).[17]
- Madagascar – Found in alluvial deposits of Betroka and Andolobe.[18] 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;[19] black sands in Nixon Fork and Wiseman districts, Alaska.[20][21]
- Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca;[22] Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.[23]
- South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal.[24]
- Democratic Republic of Congo - Kasaï region[25]
See also
edit
References
edit- ^ 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.
- ^ "Handbook of Mineralogy" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2011-12-10.
- ^ Mindat.org
- ^ Webmineral data
- ^ Frondel, C. (1958). Systematic Mineralogy of Uranium and Thorium. United States Government Printing Office.
- ^ Coomaraswamy, A.K. (1904). "Uraninite". Spolia Zeylanica. Pt. 6 (2): 57.
- ^ 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.
- ^ 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.
- ^ Kobayashi, M. (1912). "On the composition of thorianite". Tohoku Imp. Univ. Sci. Repts. 1 (Ist Ser): 201–206.
- ^ 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.
- ^ Heinrich, E. W. (1958). Mineralogy and Geology of Radioactive Raw Materials. McGraw-Hill.
- ^ Graham, A. R. (1955). "CERIANITE CeO2: A NEW RARE-EARTH OXIDE MINERAL". Am. Mineral. 40.
- ^ Bespalov, M.M. (1941). "On discovery of a new mineral of the thorianite group [in Russian]". Sovietskaya Geologiya. II (6): 105–107.
- ^ "Uranothorianite mineral information and data". Retrieved 2007-06-28.
- ^ a b "Minerals with crystal structure determined". Archived from the original on 2007-09-27. Retrieved 2007-06-27.
- ^ "ICSD for WWW : Details (Thorianite Cerian)". Retrieved 2007-06-27.[permanent dead link]
- ^ Viswanathan, P. (1953). "Thorianite in Travancore". Mineral. Mag. 88: 282.
- ^ Lacroix, A. (1923). Minéralogie de Madagascar. Augustin Challamel, éditeur, Librairie maritime et coloniale.
- ^ George, D'Arcy (1949). "Mineralogy of Uranium and Thorium Bearing Minerals". USAEC Technical Information Service, Oak Ridge, Tennessee. RMO-563: 198.
- ^ White, M. G. (1952). Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska. GS-C-195, Geological Survey.
- ^ White, M. G.; J. M. Stevens (1953). "Reconnaissance For Radioactive Deposits In The Ruby-Poorman District, Ruby Quadrangle, Central Alaska,1949". USGS Report. TEI-192, Geological Survey: 62. Bibcode:1953usgs.rept...62W. doi:10.3133/tei192.
- ^ Lang, A. H.; J. W. Griffith; H. R. Steacy (1962). Canadian Deposits of Uranium and Thorium. Geological Survey of Canada.
- ^ Robinson, S. C.; A. P. Sabina (1955). "Uraninite And Thorianite From Ontario And Quebec". Am. Mineral. 40.
- ^ Hiemstra, S. A. (1955). "Baddeleyite from Phalaborwa, Eastern Transvaal". American Mineralogist. 40: 275–282.
- ^ Ledoux, A. "Les roches cristallines du Kasai". Soc. Geol. Belgique Annales. 40: C177.
External links
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