Thorite
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.
| Thorite | |
|---|---|
Thorite crystal from the Kemp uranium mine in Ontario (size: 2.2 x 2.2 x 1.6 cm) | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | (Th,U)SiO4 |
| IMA symbol | Thr |
| Strunz classification | 9.AD.30 |
| Crystal system | Tetragonal |
| Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
| Space group | I41/amd |
| Unit cell | a = 7.13, c = 6.32 [Å]; Z = 4 |
| Identification | |
| Color | Yellow-orange, brownish yellow, brownish black, black, green |
| Crystal habit | In square prisms, or pseudo-octahedral crystals; also massive |
| Cleavage | Distinct on {110} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 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 |
| Specific gravity | 6.63 – 7.20 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.790 – 1.840 nε = 1.780 – 1.820 |
| Birefringence | δ = 0.010 – 0.020 |
| Alters to | Commonly metamict |
| Other characteristics | Radioactive |
| References | |
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