thorianite
{{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, ThO2
| molweight =
| strunz = 4.DL.05
| system = Isometric
| class = Hexoctahedral (m{{overline|3}}m)
H-M symbol: (4/m {{overline|3}} 2/m)
| symmetry = Fm3m
| unit cell = a = 5.595 Å; Z = 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 = {{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 }}[http://www.mindat.org/min-3944.html Mindat.org][http://www.webmineral.com/data/Thorianite.shtml Webmineral data]
}}
Thorianite is a rare thorium oxide mineral, ThO2.{{Cite book
| publisher = United States Government Printing Office
| last = Frondel
| first = C.
| title = Systematic Mineralogy of Uranium and Thorium
| year = 1958
}} It was originally described by Ananda Coomaraswamy in 1904 as uraninite,{{Cite journal
| volume = Pt. 6
| issue = 2
| pages = 57
| last = Coomaraswamy
| first = A.K.
| title = Uraninite
| journal = Spolia Zeylanica
| year = 1904
}} but recognized as a new species by Wyndham R. Dunstan.{{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
}} 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,{{EB1911|inline=y|wstitle=Thorianite|volume=26|page=878}} 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 {{convert|6|cm|abbr=on}}, have been reported from Madagascar.
Chemistry
Based on color, specific gravity and composition three types of thorianite are distinguished:{{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
}}
- α-thorianite
- β-thorianite
- γ-thorianite
Thorianite and uraninite form a complete solid solution series in synthetic and natural material.{{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
}} 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%.
{{Cite book
| publisher = McGraw-Hill
| last = Heinrich
| first = E. W.
| title = Mineralogy and Geology of Radioactive Raw Materials
| year = 1958
}} Rare earths, chiefly cerium, substitute for thorium in amounts up to 8% by mass.{{Cite journal
| volume = 40
| last = Graham
| first = A. R.
| title = CERIANITE CeO2: A NEW RARE-EARTH OXIDE MINERAL
| journal = Am. Mineral.
| year = 1955
}} Cerium is probably present as Ce4+. Complete series is known in synthetic material between CeO2 - PrO2 - ThO2 - UO2. Small amounts of Fe3+ 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% UO2 and 11.2% to 12.5% PbO.{{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
}}
- Uranothorianite{{Cite web
| title = Uranothorianite mineral information and data
| accessdate = 2007-06-28
| url = http://www.mindat.org/min-4114.html
}}
- Thorianite Cerian{{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
|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 }}
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).{{Cite journal
| volume = 88
| pages = 282
| last = Viswanathan
| first = P.
| title = Thorianite in Travancore
| journal = Mineral. Mag.
| year = 1953
}}
- Madagascar – Found in alluvial deposits of Betroka and Andolobe.{{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
}} 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;{{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
}} black sands in Nixon Fork and Wiseman districts, Alaska.{{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
| 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
}}
- Canada – Reported with uraninite in a pegmatite on Charlebois Lake, east of Lake Athabasca;{{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
}} Uranon variety reported from pegmatite and metesomatized zones in crystalline limestones from many locations in Quebec and Ontario.{{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
}}
- South Africa – Occurs with baddeleyite as an accessory in carbonatite at Phalaborwa, Eastern Transvaal.{{Cite journal
| volume = 40
| pages = 275–282
| last = Hiemstra
| first = S. A.
| title = Baddeleyite from Phalaborwa, Eastern Transvaal
| journal = American Mineralogist
| year = 1955
}}
| volume = 40
| pages = C177
| last = Ledoux
| first = A.
| title = Les roches cristallines du Kasai
| journal = Soc. Geol. Belgique Annales
}}
See also
{{Portal|Earth sciences}}
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]