Nesosilicate (insular SiO4 groups), zircon group, paramorph of huttonite. Thorite nearly always contains significant uranium, and most thorite is partly or completely metamict.
Thorogummite is a variety of thorite where some SiO4 has been replaced by (OH)
Specific gravity: 4.1 (with H2O) to 6.7 (no H2O) (Dana)
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
Plutonic igneous 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,
yttrialite-(Y) and pyrochlore
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.
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