Thorite

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title: "Thorite" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["thorium-minerals", "uranium(iv)-minerals", "nesosilicates", "radioactive-minerals", "tetragonal-minerals", "minerals-in-space-group-141", "minerals-described-in-1829"] description: "Nesosilicate mineral" topic_path: "general/thorium-minerals" source: "https://en.wikipedia.org/wiki/Thorite" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Nesosilicate mineral ::

::data[format=table title="infobox mineral"]

Field	Value
boxbgcolor	#926339
boxtextcolor	#fff
image	Thorite-288916.jpg
imagesize	260px
caption	Thorite crystal from the Kemp uranium mine in Ontario (size: 2.2 x 2.2 x 1.6 cm)
category	Silicate mineral
formula	(Th,U)SiO4
IMAsymbol	Thr
strunz	9.AD.30
system	Tetragonal
class	Ditetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
symmetry	I41/amd
unit cell	a = 7.13, c = 6.32 [Å]; Z = 4
color	Yellow-orange, brownish yellow, brownish black, black, green
habit	In square prisms, or pseudo-octahedral crystals; also massive
cleavage	Distinct on {110}
fracture	Conchoidal
tenacity	Brittle
mohs	4.5 – 5
luster	Vitreous to resinous
streak	Light orange to light brown sometimes even an alien magenta
diaphaneity	Nearly opaque, transparent in thin fragments
gravity	6.63 – 7.20
opticalprop	Uniaxial (−)
refractive	nω = 1.790 – 1.840 nε = 1.780 – 1.820
birefringence	δ = 0.010 – 0.020
alteration	Commonly metamict
other	[[Image:Radioactive.svg
references
::

|boxbgcolor=#926339| name = Thorite | boxtextcolor = #fff | image = Thorite-288916.jpg | imagesize = 260px | caption = Thorite crystal from the Kemp uranium mine in Ontario (size: 2.2 x 2.2 x 1.6 cm) | category = Silicate mineral | formula = (Th,U)SiO4 | IMAsymbol = Thr | molweight = | strunz = 9.AD.30 | dana = | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = I41/amd | unit cell = a = 7.13, c = 6.32 [Å]; Z = 4 | color = Yellow-orange, brownish yellow, brownish black, black, green | colour = | habit = In square prisms, or pseudo-octahedral crystals; also massive | twinning = | cleavage = Distinct on {110} | fracture = Conchoidal | tenacity = Brittle | mohs = 4.5 – 5 | luster = Vitreous to resinous | streak = Light orange to light brown sometimes even an alien magenta | diaphaneity = Nearly opaque, transparent in thin fragments | gravity = 6.63 – 7.20 | density = | polish = | opticalprop = Uniaxial (−) | refractive = nω = 1.790 – 1.840 nε = 1.780 – 1.820 | birefringence = δ = 0.010 – 0.020 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = Commonly metamict | other = [[Image:Radioactive.svg|25px]] Radioactive | prop1 = | prop1text = | references = 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. It was named in 1829 to reflect its thorium content.

Occurrence

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/dd/Thorit_1.jpg" caption="Thorite in Prague national museum"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/80/Thorites_-_CAMR_www.amrminerals.co.uk_10-crop.jpg" caption="Small 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.

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

References

1. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
2. [http://webmineral.com/data/Thorite.shtml Webmineral data]
3. [http://www.mindat.org/min-3946.html Mindat.org]
4. [http://rruff.geo.arizona.edu/doclib/hom/thorite.pdf Handbook of Mineralogy]
5. (1829). "Thorite, a new mineral, and thorina, a new earth". Philosophical Magazine.
6. (1829). "Untersuchung eines neuen Minerals und einer darin enthaltenen zuvor unbekannten Erde". Annalen der Physik und Chemie.

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