Thorite

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Thorite
Thorite-54889.jpg
idiomorphic thorite crystal from the "Kemp Uranium Mine", Cardiff, Ontario, Canada
General and classification
chemical formula (Th, U) [SiO 4 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AD.30 ( 8th edition : VIII / A.09)
05.51.02.03
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal 4 / mmm
Space group I 4 1 / amd
Lattice parameters a  = 7.13  Å ; c  = 6.32 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 4.5 to 5
Density (g / cm 3 ) 6.63 to 7.20
Cleavage after {110}
Break ; Tenacity shell-like
colour yellow-orange, brownish-yellow, brown to black, also green
Line color light orange to dark brown
transparency translucent to opaque
shine Glass gloss
radioactivity very radioactive
Crystal optics
Refractive indices n ω  = 1.790 to 1.840
n ε  = 1.780 to 1.820
Birefringence δ = 0.010 to 0.020
Optical character uniaxial negative

The mineral thorite is a rarely occurring island silicate from the zirconium group and has the chemical composition (Th, U) [SiO 4 ]. By substitution , it can contain significant amounts of other elements, particularly zirconium and uranium in place of thorium .

It crystallizes in the tetragonal crystal system and develops mostly square, prismatic or pseudo- octahedral crystals up to about 8 cm in size, but also massive aggregates of yellow-orange, brownish-yellow, brown to black, rarely also green color and light orange to dark brown line color .

Special properties

The mineral is classified as very highly radioactive due to its thorium (max. 71.6%) and uranium (depending on the degree of thorium substitution) content and has a specific activity of about 32 k Bq / g (for comparison: natural Potassium 31.2 Bq / g). Due to the high level of radioactivity, it is also often metamictic , i.e. its crystal lattice is destroyed, whereby the increasing destruction of the crystal lattice also causes the color to darken, from brown to black.

Etymology and history

Thorite was first discovered in 1828 by pastor Morten Thrane Esmark on the Norwegian island of Løvøya (Løvø) in the Langesundsfjord in the Norwegian province of Telemark and scientifically described in 1829 by Jöns Jakob Berzelius , who named the mineral after the chemical element thorium contained in the formula .

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of thorite belonged to the department of the "island silicates (nesosilicates)" where he collaborated with Coffinite , hafnon , Reidit , thorogummite and zircon formed a separate group.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the IMA, also classifies thorite in the “island silicates” department. However, this division is further subdivided according to the presence of further anions and the coordination of the cations , so that the mineral is classified according to its composition in the sub-division of “island silicates without further anions; with cations in octahedral [6] and usually greater coordination ”, where it forms together with the unnamed group 9.AD.30 .

The systematics of minerals according to Dana also assigns the thorite to the class of "silicates and germanates" and there in the department of "island silicates". There it is, also together with Coffinit, Hafnon, Thorogummit and Zirkon, in the "Zircon group" with the system no. May 51, 2002 to be found in the subsection “ Island silicates with SiO 4 groups and only with cations in> [6] coordination ”.

Modifications and varieties

The compound (Th, U) [SiO 4 ] is polymorphic , which means that it occurs in nature as a monoclinic Huttonite in addition to the tetragonal thorite .

Orangite is a crystallized, orange or yellow variety of thorite; Uranothorite with a lot of U, MacIntoshite with U and Ce , Auerlite with P instead of Si .

Education and Locations

idiomorphic thorite crystal

Thorite is a typical mineral found in granitic pegmatites that are enriched in incompatible elements . Thorite is also found in very small quantities in numerous igneous and metamorphic rocks. Accompanying minerals include zircon, monazite , gadolinite , fergusonite , uraninite , yttrialite and pyrochlore .

So far (as of 2010), Thorite has been found at around 660 sites worldwide, for example in Egypt , Armenia , Australia , Bolivia , Brazil , China , Germany , Finland , France , Greenland , Guyana , India , Indonesia , Italy , Japan , Canada , Kazakhstan , Kyrgyzstan , North and South Korea , Madagascar , Malawi , Morocco , Mexico , Mongolia , Myanmar , New Zealand , Nigeria , Norway , Austria , Pakistan , Paraguay , Poland , Portugal , Russia , Zambia , Saudi Arabia , Sweden , Slovakia , Spain , Swaziland , South Africa , Tajikistan , Czech Republic , Ukraine , Hungary and the United States of America (USA).

Crystal structure

Thorite crystallizes tetragonally in the space group I 4 1 / amd with the lattice parameters a  = 7.13  Å and c  = 6.32 Å as well as 4 formula units per unit cell .

See also

Individual evidence

  1. ↑ a b Webmineral - Thorite (English)
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 543 .
  3. ↑ a b Thorite at mindat.org (engl.)
  4. ↑ JJ Berzelius: About the thorite, a new mineral, and a new earth contained in it, the gate earth . In: Annalen der Physik (1829, Volume 91, Issue 4, pp. 633–634)
  5. ↑ Mindat - Localities for thorite

literature

See also

Web links

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