Formula: Th(SiO4)
Nesosilicate (insular SiO4 groups), zircon group, dimorph of huttonite. Thorite nearly always contains significant uranium, and most thorite is partly or completely metamict.
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)

Plutonic igneous environments
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 and pyrochlore (HOM, Dana).

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.

Common impurities: Al,Fe,Pb,Ca,P,Ti,REE,Y,Mg,H2O

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