Thorianite

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Thorianite
Thorianite-54888.jpg
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
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
Other characteristics Radioactive.svg 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.

Contents

Chemistry

Based on color, specific gravity and composition three types of thorianite are distinguished: [9]

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

Occurrence

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

See also

Related Research Articles

<span class="mw-page-title-main">Uraninite</span> Uranium-rich oxide mineral

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

<span class="mw-page-title-main">Pyrochlore</span> Niobium mineral of A2B2O7 general formula

Pyrochlore2Nb2O6(OH,F) is a mineral group of the niobium end member of the pyrochlore supergroup. The general formula, A2B2O7, represent a family of phases isostructural to the mineral pyrochlore. Pyrochlores are an important class of materials in diverse technological applications such as luminescence, ionic conductivity, nuclear waste immobilization, high temperature thermal barrier coatings, automobile exhaust gas control, catalysts, solid oxide fuel cell, ionic/electrical conductors etc.

<span class="mw-page-title-main">Euxenite</span> Oxide mineral

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

<span class="mw-page-title-main">Gadolinite</span> Nesosilicate mineral

Gadolinite, sometimes known as ytterbite, is a silicate mineral consisting principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with the formula (Ce,La,Nd,Y)2FeBe2Si2O10. It is called gadolinite-(Ce) or gadolinite-(Y), depending on the prominent composing element. It may contain 35.5% yttria sub-group rare earths, 2.2% ceria earths, as much as to 11.6% BeO, and traces of thorium. It is found in Sweden, Norway, and the US.

<span class="mw-page-title-main">Monazite</span> Mineral containing rare-earth elements

Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the cerium-dominant member of the group. 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 five different most common species of monazite, depending on the relative amounts of the rare earth elements in the mineral:

<span class="mw-page-title-main">Coffinite</span>

Coffinite is a uranium-bearing silicate mineral with formula: U(SiO4)1−x(OH)4x.

<span class="mw-page-title-main">Autunite</span>

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.

<span class="mw-page-title-main">Thorite</span>

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.

<span class="mw-page-title-main">Zippeite</span>

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 under ultraviolet light and is moderately radioactive.

<span class="mw-page-title-main">Xenotime</span> Phosphate mineral

Xenotime is a rare-earth phosphate mineral, the major component of which is yttrium orthophosphate (YPO4). It forms a solid solution series with chernovite-(Y) (YAsO4) and therefore may contain trace impurities of arsenic, as well as silicon dioxide and calcium. The rare-earth elements dysprosium, erbium, terbium and ytterbium, as well as metal elements such as thorium and uranium (all replacing yttrium) are the expressive secondary components of xenotime. Due to uranium and thorium impurities, some xenotime specimens may be weakly to strongly radioactive. Lithiophyllite, monazite and purpurite are sometimes grouped with xenotime in the informal "anhydrous phosphates" group. Xenotime is used chiefly as a source of yttrium and heavy lanthanide metals (dysprosium, ytterbium, erbium and gadolinium). Occasionally, gemstones are also cut from the finest xenotime crystals.

<span class="mw-page-title-main">Carbonatite</span> 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.

<span class="mw-page-title-main">Uranium ore</span> 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.

<span class="mw-page-title-main">Betafite</span> Mineral group

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. Originally defined by the B-site atom Ti, the development of new nomenclature for mineral names led to modernization of the system for nomenclature of pyrochlore and betafite in order to further rationalize the naming process of this grouping of minerals. Only two of the mineral species that were formerly recognized as betafite are presently retained. They are oxyuranobetafite and oxycalciobetafite. The term betafite is now a synonym or varietal group name under the pyrochlore super group.

<span class="mw-page-title-main">Johannite</span>

Johannite is a rare uranium sulfate mineral. It crystallizes in the triclinic crystal system with the chemical composition Cu[UO2(OH)SO4]2·8H2O. It crystallizes in the triclinic system and develops only small prism or thin to thick tabular crystals, usually occurs as flaky or spheroidal aggregates and efflorescent coatings. Its color is emerald-green to apple-green and its streak is pale green.

<span class="mw-page-title-main">Stillwellite-(Ce)</span>

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

<span class="mw-page-title-main">Boltwoodite</span> 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.

Uranpyrochlore , also known as ellsworthite or betafite(Ca,U)2(Ti,Nb,Ta)2O6(OH) is a rare earth mineral mostly found in the northern parts of North America. It is a uranpyrochlore and is named after Hardy V. Ellsworth of the Canadian Geological Survey by Walker and Parsons. It is a very uranium- and thorium- rich mineral, which in fact makes it slightly radioactive. Uranium makes up about 17.1% of the mineral. Ellsworthite is also known as the mineral Betafite. Ellsworthite is a thorium-bearing mineral that is found mostly in Canada and Alaska. It was first discovered in Hybla, Ontario, which is now a ghost town.

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.

<span class="mw-page-title-main">Occurrence of thorium</span>

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.

References

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  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. Wikisource-logo.svg 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.
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