Thorite

Short description: Nesosilicate mineral

Thorite

Thorite crystal from the Kemp uranium mine in Ontario (size: 2.2 x 2.2 x 1.6 cm)

General
Category| Silicate mineral
Formula
(repeating unit)| (Th,U)SiO4
Strunz classification| 9.AD.30
Crystal system| Tetragonal
Crystal class| Ditetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space group| I41/amd
Unit cell| a = 7.13, c = 6.32 [Å]; Z = 4
Identification
Color| Yellow-orange, brownish yellow, brownish black, black, green
Crystal habit| In square prisms, or pseudo-octahedral crystals; also massive
Cleavage| Distinct on {110}
Fracture| Conchoidal
Tenacity| Brittle
Mohs scale hardness| 4.5 – 5
|re|er}}| Vitreous to resinous
Streak| Light orange to light brown sometimes even an alien magenta
Diaphaneity| Nearly opaque, transparent in thin fragments
Specific gravity| 6.63 – 7.20
Optical properties| Uniaxial (−)
Refractive index| nω = 1.790 – 1.840 nε = 1.780 – 1.820
Birefringence| δ = 0.010 – 0.020
Alters to| Commonly metamict
Other characteristics|  Radioactive
References| [1][2][3]

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. Thorite was discovered in 1828 on the island of Løvøya, Norway, by the vicar and mineralogist, Hans Morten Thrane Esmark. First specimens of Thorite were sent to his father, Jens Esmark, who was a professor of mineralogy and geology.[5][6][7] It was named in 1829 to reflect its thorium content.

## Contents

* 1 Occurrence
* 2 Properties
* 3 References
* 4 External links

## Occurrence

Thorite in Prague national museum Error creating thumbnail: Unable to save thumbnail to destinationSmall crystals of green thorite under magnification

Specimens of thorite generally come from igneous pegmatites and volcanic extrusive rocks, hydrothermal veins and contact metamorphic rocks. It is also known to occur as small grains in detrital sands. Crystals are rare, but when found can produce nicely shaped short prismatic crystals with pyramidal terminations. It is commonly associated with zircon, monazite, gadolinite, fergusonite, uraninite, yttrialite and pyrochlore.[3]

Thorite is currently an important ore of uranium. A variety of thorite, often called "uranothorite", is particularly rich in uranium and has been a viable uranium ore at Bancroft in Ontario, Canada. Other varieties of thorite include "orangite", an orange variety, and "calciothorite", an impure variety with trace amounts of calcium.

## Properties

Due to the radioactive elements contained, Thorite is commonly metamict. With the destructive effects of radioactivity on the crystal lattice, hydrated specimens are often amorphous and optically isotropic. Owing to differences in composition, the specific gravity varies from 4.4 to 6.6 g/cm3. Hardness is 4.5 and the luster is vitreous or resinous. The color is normally black, but can range from brownish black to orange, yellowish-orange and dark green.

## References

1. ↑ Webmineral data
2. ↑ Mindat.org
3. ↑ 3.0 3.1 Handbook of Mineralogy
4. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
5. ↑ Berzelius, M. (1829). "Thorite, a new mineral, and thorina, a new earth". Philosophical Magazine. Series 2 6 (35): 392–393. doi:10.1080/14786442908675174. https://zenodo.org/record/1430987.
6. ↑ Berzelius, J. J. (1829). "Untersuchung eines neuen Minerals und einer darin enthaltenen zuvor unbekannten Erde". Annalen der Physik und Chemie 92 (7): 385–415. doi:10.1002/andp.18290920702. Bibcode: 1829AnP....92..385B. https://zenodo.org/record/1423530.
7. ↑ Marshall, J.L.; Marshall, V.R. (2001). "Rediscovery of the Elements- Thorium-Løvøya, Langesundsfjord, Norway". The Hexagon 93: 70–73. Archived from the original on 2005-04-08. https://web.archive.org/web/20050408114055/http://www.chem.unt.edu/Rediscovery/Thorium.pdf.

## External links

| Wikisource has the text of the 1911 Encyclopædia Britannica article Thorite.

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