Thorite, (Th,U)SiO<sub>4</sub>, 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
thumb|left|Thorite in Prague national museum
thumb|left|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.