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Group of interpenetrating twinned thorianite crystals from Ambatofotsy, Madagascar (size: 1.6 x 1.4 x 1.3 cm)
Category Oxide mineral
(repeating unit)
Thorium oxide, ThO2
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
ColorDark 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 hardness6.5 – 7
Luster Resinous, sub-metallic
Streak Grey, grey green to black
Diaphaneity Opaque, translucent on thin edges
Specific gravity 9.7
Optical propertiesIsotropic
Refractive index n = 2.20 – 2.35
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 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, 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.

Thorium Chemical element with atomic number 90

Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately hard, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

Ananda Coomaraswamy Ceylonese philosopher and early interpreter of Indian culture to the West

Ananda Kentish Muthu Coomaraswamy was a Sri Lankan Tamil metaphysician, pioneering historian and philosopher of Indian art who was an early interpreter of Indian culture to the West. In particular, he is described as "the groundbreaking theorist who was largely responsible for introducing ancient Indian art to the West."

Sir Wyndham Rowland Dunstan (1861-1949), was professor of chemistry and Director of the Imperial Institute in London.



Based on color, specific gravity and composition three types of thorianite are distinguished: [7]

Thorianite and uraninite form a complete solid solution series in synthetic and natural material. [8] 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 87.9%. [9] Rare earths, chiefly Ce, substitute for Th in amounts up to 8% by weight. [8] [10] 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.

Uraninite oxide mineral

Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but due to oxidation the mineral typically contains variable proportions of U3O8. Additionally, due to radioactive decay, the ore also contains oxides of lead and trace amounts of helium. It may also contain thorium and rare earth elements.

Solid solution Chemical solution in solid form; whose solvents crystal structure is not altered by solute

A solid solution is a solid-state solution of one or more solutes in a solvent. Such a multi-component system is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the chemical components remain in a single homogeneous phase. This often happens when the two elements involved are close together on the periodic table; conversely, a chemical compound generally results when two metals involved are not near each other on the periodic table.



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

Galle City in Southern Province, Sri Lanka

Galle is a major city in Sri Lanka, situated on the southwestern tip, 119 km from Colombo. Galle is the administrative capital of Southern Province, Sri Lanka and is the district capital of Galle District.

Balangoda Town in Sabaragamuwa Province, Sri Lanka

Balangoda is a large town in Ratnapura District, Sabaragamuwa Province, Sri Lanka, governed by an urban council located 143 kilometres (89 mi) away from Colombo and 43 kilometres (27 mi) from Ratnapura on Colombo - Batticaloa Highway(A4). It is one of the largest towns of the Sabaragamuwa Province. According to the 2001 census, Balangoda has a population of 16,875 and area of 16.2 km2.

India Country in South Asia

India is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the north; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives; its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia.

See also

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Pyrochlore mineral group, pyrochlore supergroup

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Baddeleyite oxide mineral

Baddeleyite is a rare zirconium oxide mineral (ZrO2 or zirconia), occurring in a variety of monoclinic prismatic crystal forms. It is transparent to translucent, has high indices of refraction, and ranges from colorless to yellow, green, and dark brown. See etymology below.

Euxenite oxide mineral

Euxenite or euxenite-(Y) is a brownish black mineral with a metallic luster.

Monazite phosphate mineral series

Monazite is a reddish-brown phosphate mineral containing rare-earth metals. It occurs usually in small isolated crystals. It has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3. There are at least four different kinds of monazite, depending on relative elemental composition of the mineral:

Autunite uranyl phosphate mineral

Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–​2 12. Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals, commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.

Thorite nesosilicate mineral

Thorite, (Th,U)SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to reflect its thorium content. Thorite was discovered in 1828 on the island of Løvøya, Norway, by the vicar and mineralogist, Hans Morten Thrane Esmark, who sent the first specimens of this black mineral to his father, Jens Esmark, who was a professor of mineralogy and geology.

Zippeite uranyl sulfate mineral

Zippeite is a hydrous potassium uranium sulfate mineral with formula: K4(UO2)6(SO4)3(OH)10·4(H2O). It forms yellow to reddish brown monoclinic-prismatic crystals with perfect cleavage. The typical form is as encrustations and pulverulent earthy masses. It forms as efflorescent encrustations in underground uranium mines. It has a Mohs hardness of 2 and a specific gravity of 3.66. It is strongly fluorescent yellow in UV radiation and is a radioactive mineral.

Carbonatite Igneous rock with more than 50% carbonate minerals

Carbonatite is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification.

Ore genesis How the various types of mineral deposits form within the Earths crust.

Various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.

Cafetite hydroxide mineral

Cafetite is a rare titanium oxide mineral with formula (Ca,Mg)(Fe,Al)2Ti4O12·4(H2O). It is named for its composition, Ca-Fe-Ti.

Uranium ore economically recoverable concentrations of uranium within the Earths crust

Uranium ore deposits are economically recoverable concentrations of uranium within the Earth's crust. Uranium is one of the more common elements in the Earth's crust, being 40 times more common than silver and 500 times more common than gold. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge for commercial uranium extraction is to find those areas where the concentrations are adequate to form an economically viable deposit. The primary use for uranium obtained from mining is in fuel for nuclear reactors.

Betafite mineral group, pyrochlore supergroup

Betafite is a mineral group in the pyrochlore supergroup, with the chemical formula (Ca,U)2(Ti,Nb,Ta)2O6(OH). Betafite typically occurs as a primary mineral in granite pegmatites, rarely in carbonatites. Defined by the B-site atom Ti, Atencio et al.(2010) combined and considered the ideas portrayed in (Hatert and Burke)(2008) and a modernization of (Hogarth)(1977) system for nomenclature of pyrochlore and betafite in order to further rationalize the naming process of this grouping of minerals. Therefore, Atencio et al. (2010), states that only two of the mineral species that were formerly recognized under the previous nomenclature system of betafite in Hogarth (1977) are now recognized. They are oxyuranobetafite and oxycalciobetafite. Now the term betafite is a synonym or varietal group name under the pyrochlore super group (Christy and Atencio 2013).

Stillwellite-(Ce) nesosilicate mineral

Stillwellite-(Ce) is a rare-earth boro-silicate mineral with formula: (Ce,La,Ca)BSiO5.

Boltwoodite hydrated potassium uranyl silicate mineral

Boltwoodite is a hydrated potassium uranyl silicate mineral with formula HK(UO2)(SiO4)·1.5(H2O). It is formed from the oxidation and alteration of primary uranium ores. It takes the form of a crust on some sandstones that bear uranium. These crusts tend to be yellowish with a silky or vitreous luster.

Paulscherrerite, UO2(OH)2, is a newly named mineral of the schoepite subgroup of hexavalent uranium hydrate/hydroxides. It is monoclinic, but no space group has been determined because no single-crystal study has been done. Paulscherrerite occurs as a canary yellow microcrystalline powdery product with a length of ~500 nm. It forms by the weathering and ultimate pseudomorphism of uranium-lead bearing minerals such as metaschoepite. The type locality for paulscherrerite is the Number 2 Workings, Radium Ridge near Mount Painter, North Flinders Ranges, South Australia, an area where radiogenic heat has driven hydrothermal activity for millions of years. It is named for Swiss physicist Paul Scherrer, co-inventor of the Debye-Scherrer X-ray powder diffraction camera. Study of paulscherrerite and related minerals is important for understanding the mobility of uranium around mining sites, as well as designing successful strategies for the storage of nuclear weapons and the containment of nuclear waste.

Occurrence of thorium

Thorium is found in small amounts in most rocks and soils. Soil commonly contains an average of around 6 parts per million (ppm) of thorium. Thorium occurs in several minerals including thorite (ThSiO4), thorianite (ThO2 + UO2) and monazite. Thorianite is a rare mineral and may contain up to about 12% thorium oxide. Monazite contains 2.5% thorium, allanite has 0.1 to 2% thorium and zircon can have up to 0.4% thorium. Thorium-containing minerals occur on all continents. Thorium is several times more abundant in Earth's crust than all isotopes of uranium combined and thorium-232 is several hundred times more abundant than uranium-235.

Grayite, ThPO4 • (H2O), is a thorium phosphate mineral of the Rabdophane group first discovered in 1957 by S.H.U. Bowie in Rhodesia. It is of moderate hardness occurring occasionally in aggregates of hexagonal crystals occasionally but more commonly in microgranular/cryptocrystalline masses. Due to its thorium content, grayite displays some radioactivity although it is only moderate and the mineral displays powder XRD peaks without any metamict-like effects. The color of grayite is most commonly observed as a light to dark reddish brown but has also been observed as lighter yellows with grayish tints. It has a low to moderate hardness with a Mohs hardness of 3-4 and has a specific gravity of 3.7-4.3. It has been found in both intrusive igneous and sedimentary environments.

Cerianite-(Ce) is a relatively rare oxide mineral, belonging to uraninite group with the formula (Ce,Th)O2. It is one of a few currently known minerals containing essential tetravalent cerium, the other examples being stetindite and dyrnaesite-(La).


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