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Formula: Th(SiO4)
Nesosilicate (insular SiO4 groups), zircon group,
paramorph of
huttonite. Thorite nearly always contains significant uranium, and most thorite is
partly or completely metamict.
Varieties
Thorogummite is a variety of thorite where some SiO4 has been replaced by (OH)
Uranothorite is a variety of thorite rich in uranium
Properties
Crystal System: Tetragonal
Specific gravity: 4.1 (with H2O) to 6.7 (no H2O) (Dana)
Hardness: 4½
Streak: Light brown
Colour: Yellow, yellow-brown, red-brown, green, orange to black
Solubility: Fresh material is insoluble in common acids; metamict material is attacked by hot acids (Dana)
Common impurities: Al,Fe,Pb,Ca,P,Ti,REE,Y,Mg,H2O
RADIOACTIVE
Environments
Plutonic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments
Thorite is a widespread primary mineral; it occurs in
granite, granitic pegmatites,
augite syenite rocks, metasomatised zones in
impure limestone, hydrothermal veins and detrital deposits
(Dana, Webmin, HOM).
Associated minerals include zircon,
monazite,
allanite, gadolinite,
fergusonite, uraninite,
yttrialite-(Y) and pyrochlore
(HOM, Dana).
Localities
At the Trimouns quarry, Luzenac, Ariège, France, thorite has been found very rarely in the mica
schist of the pegmatite zone in the footwall of the
talc-chlorite structure
(MinRec 35.3.243).
The type locality is the Thorite Hole, Løvøya, Langesundsfjorden, Porsgrunn, Telemark, Norway.
At Rose Road, Pitcairn, St. Lawrence county, New York, USA, thorite mineralisation fluoresces brilliant green
both from pieces of the original pod and from patchy coatings on the surfaces of other minerals that were down slope
from the pod in fractured areas or as loose pieces in the scree
(R&M 97.5.442).
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