Thorianite

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Thorianite
Thorianite-54888.jpg
Thorianite triplet from Soavinandriana ( Itasy region ) in Madagascar
General and classification
chemical formula ThO 2
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DL.05 ( 8th edition : IV / D.31)
01/05/01/02
Similar minerals Uraninite , cerite (not radioactive)
Crystallographic Data
Crystal system cubic
Crystal class ; symbol hexakisoctahedral 4 / m 3 2 / m
Space group Fm 3 m
Lattice parameters a  = 5.5997  Å
Formula units Z  = 4
Twinning Penetrating twins often
Physical Properties
Mohs hardness 6.5 to 7
Density (g / cm 3 ) 8.5 to 9.87
Cleavage imperfect after {100}, {010} and {001}
Break ; Tenacity shell-like to uneven, brittle
colour gray-green, yellow-brown, brownish-black to black, greenish to brownish internal reflections
Line color pale brown, white
transparency opaque, splinters and thinnest layers, etc. U. translucent
shine Greasy sheen to strong diamond sheen, more rarely semi-metallic, unrolled pieces have a waxy sheen
radioactivity highly radioactive

Thorianite (chemically: thorium dioxide ) is a rather seldom occurring mineral from the mineral class of oxides and hydroxides. It crystallizes in the cubic crystal system with the chemical composition ThO 2 and develops mostly cubic crystals , which rarely show octahedron faces at the corners. Thorianites from river deposits, on the other hand, can have an extremely inconspicuous appearance. Their matt, washed-out shine then resembles that of black polished stones. Only the density and radioactivity show in such cases that it is not an ordinary stone.

Thorianite forms a perfect mixed series with uraninite . Due to the good miscibility of both minerals, the thorium can be replaced by uranium in any ratio .

Special properties

Thorianite is classified as very radioactive due to its thorium content of up to 88% and has a specific activity of around 39.4 k Bq / g (for comparison: natural potassium 31.2 Bq / g). Despite their high level of radioactivity, thorianites resist isotropization, that is to say the metamorphic destruction of the crystal lattice by their own radiation, better than most other uranium and thorium-containing minerals.

Its melting point is unusually high at 3390 ° C, although contaminated pieces sometimes have very different melting points.

The mineral is diamagnetic , so it has a tendency to move out of a magnetic field .

Etymology and history

Thorianite was first found in 1904 near Balangoda (Sabaragamuwa Province) in Sri Lanka and described by Wyndham R. Dunstan, who named the mineral after its thorium content .

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the thorianite belongs to the division of "oxides with the molar ratio metal: oxygen = 1: 2". The 9th edition of Strunz's system, however, now subdivides this section more precisely according to the size of the cations involved and the crystal structure and the mineral can be found accordingly in the subsection “ With large (± medium-sized) cations and structures typical of fluorite ”.

The systematics of minerals according to Dana also sorts thorianite into the class of oxides, but there in the subdivision of "uranium and thorium-containing oxides with a cation charge of 4+ and the general formula (AO 2 )".

Modifications and varieties

Uranothorianite is the uranium-containing variety of thorianite.

Education and Locations

several large thorianite cubes from Galle in Sri-Lanka ( Ceylon )

Thorianite rarely forms larger deposits. As a rule, it forms isolated crystals and, less often, small crystal groups in pegmatites and some metamorphic deposits. During weathering and natural erosion of the bedrock, the relatively resistant crystals are transported away and can accumulate in alluvial deposits (including so-called soaps ).

One of the most famous locations for uranium-containing thorianite (so-called uranothorianite) is Esiva in the province of Toliara (Tuléar) on Madagascar , where it occurred in crystals up to 2.5 cm in size.

Thorianite has been detected at 124 sites worldwide (as of 2009), including Badachschan in Afghanistan; in the northeast to eastern desert on the Red Sea in Egypt; Tasmania and Victoria in Australia; Minas Gerais and Pará in Brazil; Hebei , Jiangxi and Liaoning in China; near Kruft and Mendig (Eifel) in Germany; at Narsaq in Greenland; several provinces of Italy ; Nunavut , Ontario and Quebec in Canada; Chöwsgöl-Aimag (Hövsgöl) in Mongolia; Alto Ligonha in Mozambique ; Akershus , Aust-Agder and Telemark in Norway; Eastern Siberia , Kola and Urals in Russia; Småland in Sweden; near Košice in Slovakia; in Spanish Catalonia ; near Phalaborwa and Sutherland (South Africa) ; Moravia in the Czech Republic; Fejér and Tolna in Hungary; as well as many regions of the USA .

Crystal structure

Thorianite crystallizes in the cubic crystal system in the space group F m3m with the lattice parameter a  = 5.5997  Å and four formula units per unit cell , so it has a crystal structure that is similar to that of fluorite .

use

Due to its mostly low enrichment, thorianite is only rarely used to extract thorium. This is also due to the currently low demand for thorium. Therefore, thorianite is rarely mined for thorium extraction. Uranothorianites are still occasionally mined mainly for the extraction of uranium. Together with other minerals ( Monazite, etc.), the promotion is more worthwhile. Uranothorianite from Madagascar was mined from the end of the 50s to the beginning of the 70s mainly for the extraction of uranium. Current exploratory work (deep drilling) has shown that uranothorianite mineralization can also be traced further into the depths (in November 2007 up to approx. 80 m with core drilling).

Precautions

It is advisable to wash your hands after each touch. Storage in transparent plastic boxes intended for collecting purposes is particularly useful for small items. Buying large quantities of small, loose pieces, such as those that are sometimes offered, is not recommended because of the dust formation and the long range of the radiation. Smaller individual pieces in normal quantities, however, are less of a concern.

See also

Individual evidence

  1. ↑ a b c d Webmineral - Thorianite .
  2. ↑ a b American Mineralogist Crystal Structure Database - Thorianite (English, 1963).
  3. ↑ Wyndham R. Dunstan: The occurrence of Thorium in Ceylon . In: Nature . 69, March 31, 1904, pp. 510-511.
  4. ↑ Mindat - Localities for Thorianite .
  5. ↑ American Mineralogist Crystal Structure Database - Thorianite (English, 1963).
  6. ^ Pan African Mining Corp .: Further Core Drilling Results from Pan African's Tranomaro Uranium Project Confirm Extension of Zone to the South; Intersects Include 10.0 M of 2.34 Lbs./SH.T U3O8 ( Memento from September 13, 2011 in the Internet Archive ) from November 28, 2007.

literature

Web links

Commons : Thorianite  - collection of images, videos and audio files