{{Short description|Thorium oxide mineral}} {{Infobox mineral |boxbgcolor=#6d625d| name = Thorianite | boxtextcolor = #fff | category = Oxide mineral | image = Thorianite-54888.jpg | caption = Group of interpenetrating twinned thorianite crystals from Ambatofotsy, Madagascar (size: 1.6 x 1.4 x 1.3 cm) | formula = Thorium oxide, ThO<sub>2</sub> | IMAsymbol = Tho<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 4.DL.05 | system = Isometric | class = Hexoctahedral (m{{overline|3}}m) <br/>H-M symbol: (4/m {{overline|3}} 2/m) | symmetry = ''Fm3m'' | unit cell = a = 5.595&nbsp;Å; Z&nbsp;=&nbsp;4 | color = Dark gray, brown-black | 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 = 6.5 – 7 | luster = Resinous, sub-metallic | refractive = n = 2.20 – 2.35 | opticalprop = Isotropic | birefringence = | pleochroism = | streak = Grey, grey green to black | gravity = 9.7 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque, translucent on thin edges | other = 25px Radioactive | references = <ref name=HBM>{{Cite web |url=http://www.handbookofmineralogy.com/pdfs/thorianite.pdf |title=Handbook of Mineralogy |access-date=2011-12-10 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303170830/http://www.handbookofmineralogy.com/pdfs/thorianite.pdf |url-status=dead }}</ref><ref name=Mindat>[http://www.mindat.org/min-3944.html Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Thorianite.shtml Webmineral data]</ref> }}

'''Thorianite''' is a rare thorium oxide mineral, ThO<sub>2</sub>.<ref>{{Cite book | publisher = United States Government Printing Office | last = Frondel | first = C. | title = Systematic Mineralogy of Uranium and Thorium | year = 1958 }}</ref> It was originally described by Ananda Coomaraswamy in 1904 as uraninite,<ref>{{Cite journal | volume = Pt. 6 | issue = 2 | pages = 57 | last = Coomaraswamy | first = A.K. | title = Uraninite | journal = Spolia Zeylanica | year = 1904 }}</ref> but recognized as a new species by Wyndham R. Dunstan.<ref>{{Cite journal | volume = 69 | pages = 510–511 | last = Dunstan | first = Wyndham R. | title = The occurrence of Thorium in Ceylon | journal = Nature | date = 1904-03-31 | doi = 10.1038/069510d0 | issue=1796 |bibcode = 1904Natur..69..510D | s2cid = 4032255 | url = https://zenodo.org/record/1429437 | doi-access = free }}</ref> 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,<ref name="EB1911">{{EB1911|inline=y|wstitle=Thorianite|volume=26|page=878}}</ref> 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&nbsp;cm. Larger crystals, up to {{convert|6|cm|abbr=on}}, have been reported from Madagascar.

==Chemistry== Based on color, specific gravity and composition three types of thorianite are distinguished:<ref>{{Cite journal | volume = 1 | issue = Ist Ser | pages = 201–206 | last = Kobayashi | first = M. | title = On the composition of thorianite | journal = Tohoku Imp. Univ. Sci. Repts. | year = 1912 }}</ref> *α-thorianite *β-thorianite *γ-thorianite Thorianite and uraninite form a complete solid solution series in synthetic and natural material.<ref name=Dana>{{Cite book | pages = 620–622 | last = Palache | first = C. |author2=H. Berman |author3=C. Frondel | title = Dana's System of Mineralogy, Volume 1 | publisher = John Wiley and Sons, New York | year = 1944 }}</ref> The division between the two species is at Th:U = 1:1 with uranium possibly making up to 46.50% and thorium ranging up to 87.88%.<ref> {{Cite book | publisher = McGraw-Hill | last = Heinrich | first = E. W. | title = Mineralogy and Geology of Radioactive Raw Materials | year = 1958 }}</ref> Rare earths, chiefly cerium, substitute for thorium in amounts up to 8% by mass.<ref name=Dana/><ref>{{Cite journal | volume = 40 | last = Graham | first = A. R. | title = CERIANITE CeO<sub>2</sub>: A NEW RARE-EARTH OXIDE MINERAL | journal = Am. Mineral. | year = 1955 }}</ref> Cerium is probably present as Ce<sup>4+</sup>. Complete series is known in synthetic material between CeO<sub>2</sub> - PrO<sub>2</sub> - ThO<sub>2</sub> - UO<sub>2</sub>. Small amounts of Fe<sup>3+</sup> and zirconium also may be isomorphous with thorium. Lead present is probably radiogenic.

==Varieties== *''Aldanite'' – a variety of thorianite containing 14.9% to 29.0% UO<sub>2</sub> and 11.2% to 12.5% PbO.<ref>{{Cite journal | volume = II | issue = 6 | pages = 105–107 | last = Bespalov | first = M.M. | title = On discovery of a new mineral of the thorianite group [in Russian] | journal = Sovietskaya Geologiya | year = 1941 }}</ref> *''Uranothorianite''<ref>{{Cite web | title = Uranothorianite mineral information and data | accessdate = 2007-06-28 | url = http://www.mindat.org/min-4114.html }}</ref> *''Thorianite Cerian''<ref name=var>{{Cite web |title = Minerals with crystal structure determined |accessdate = 2007-06-27 |url = http://sdpd.univ-lemans.fr/minknown.html#T |url-status = dead |archiveurl = https://web.archive.org/web/20070927022021/http://sdpd.univ-lemans.fr/minknown.html#T |archivedate = 2007-09-27 }}</ref><ref>{{Cite web |title = ICSD for WWW : Details (Thorianite Cerian) |accessdate = 2007-06-27 |url = http://icsdweb.fiz-karlsruhe.de/details.php?id%5B%5D=24439&PHPSESSID=734118bb8 }}{{Dead link|date=June 2018 |bot=InternetArchiveBot |fix-attempted=no }}</ref> *''Thorianite La bearing''<ref name=var/>

==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).<ref>{{Cite journal | volume = 88 | pages = 282 | last = Viswanathan | first = P. | title = Thorianite in Travancore | journal = Mineral. Mag. | year = 1953 }}</ref> *Madagascar – Found in alluvial deposits of Betroka and Andolobe.<ref>{{Cite book | publisher = Augustin Challamel, éditeur, Librairie maritime et coloniale | last = Lacroix | first = A. | title = Minéralogie de Madagascar | url = https://archive.org/details/MineralogieDeMadagascarTome3 | year = 1923 }}</ref> 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;<ref>{{Cite journal | pages = 198 | last = George | first = D'Arcy | title = Mineralogy of Uranium and Thorium Bearing Minerals | journal = USAEC Technical Information Service, Oak Ridge, Tennessee | series = RMO-563 | year = 1949 }}</ref> black sands in Nixon Fork and Wiseman districts, Alaska.<ref>{{Cite book | publisher = GS-C-195, Geological Survey | last = White | first = M. G. | title = Radioactivity of Selected Rocks and Placer Concentrates from Northeastern Alaska | year = 1952 }}</ref><ref>{{Cite journal | publisher = TEI-192, Geological Survey | last = White | first = M. G. |author2=J. M. Stevens | title = Reconnaissance For Radioactive Deposits In The Ruby-Poorman District, Ruby Quadrangle, Central Alaska,1949 | journal = USGS Report | year = 1953 | page = 62 | doi = 10.3133/tei192 | bibcode = 1953usgs.rept...62W | url = https://digital.library.unt.edu/ark:/67531/metadc1050378/m2/1/high_res_d/report.pdf }}</ref> *Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca;<ref>{{Cite book | publisher = Geological Survey of Canada | last = Lang | first = A. H. |author2=J. W. Griffith |author3=H. R. Steacy | title = Canadian Deposits of Uranium and Thorium | year = 1962 }}</ref> Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.<ref>{{Cite journal | volume = 40 | last = Robinson | first = S. C. |author2=A. P. Sabina | title = Uraninite And Thorianite From Ontario And Quebec | journal = Am. Mineral. | year = 1955 }}</ref> *South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal.<ref>{{Cite journal | volume = 40 | pages = 275–282 | last = Hiemstra | first = S. A. | title = Baddeleyite from Phalaborwa, Eastern Transvaal | journal = American Mineralogist | year = 1955 }}</ref> *Democratic Republic of Congo - Kasaï region<ref>{{Cite journal | volume = 40 | pages = C177 | last = Ledoux | first = A. | title = Les roches cristallines du Kasai | journal = Soc. Geol. Belgique Annales }}</ref>

==See also== {{Portal|Earth sciences}} * Uraninite * Thorite * Classification of minerals * List of minerals

==References== {{reflist | 2}}

==External links== {{Commons category}} * [https://web.archive.org/web/20070703180719/http://www.uraniumminerals.com/UTh/Thorianite.htm Uraniumminerals.com] * [http://www.mindat.org/min-3944.html Mindat.org]

Category:Thorium minerals Category:Oxide minerals Category:Minerals described in 1904 Category:Radioactive minerals Category:Cubic minerals Category:Minerals in space group 225