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Fluocerite, also known as tysonite, is a mineral consisting of cerium and lanthanum fluorides, with the chemical formula (Ce,La)F3.[1][2] The end members are classified as two different mineral types depending on the cation, fluocerite-(Ce) and fluocerite-(La), corresponding respectively to lanthanum trifluoride and cerium trifluoride. Both crystallize in the trigonal system.[3]
| Fluocerite-(La) | |
|---|---|
| General | |
| Category | Mineral |
| Formula (repeating unit) | (La,Ce)F3 |
| Strunz classification | 03.AC.15 (03) |
| Dana classification | 09.03.04.02 (09) |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral |
| Space group | P3c1 (No. 165) |
| Unit cell | 328.80 ų (Calculated from Unit Cell) |
| Identification | |
| Formula mass | 196.02 |
| Colour | Greenish-yellow |
| Crystal habit | Platy, tabular |
| Cleavage | Indistinct, Imperfect |
| Mohs scale hardness | 4-5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Density | 5.93 |
| Birefringence | 0.006 |
| Fluocerite-(Ce) | |
|---|---|
| General | |
| Category | Mineral |
| Formula (repeating unit) | (La,Ce)F3 |
| Strunz classification | 3/A.10-20 |
| Dana classification | 9.3.4.1 |
| Crystal system | Trigonal |
| Crystal class | Hexagonal Scalenohedral |
| Unit cell | 320.86 ų (Calculated from Unit Cell) |
| Identification | |
| Formula mass | 196.99 |
| Colour | Light yellow; darkening to yellow- and red-brown; colourless to pale pink (transmitted light) |
| Crystal habit | Massive, Primsatic |
| Cleavage | Distinct/Good |
| Fracture | Irregular/Uneven, Splintery, Sub-Conchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 4.5-5 |
| Luster | Vitreous, Resinous, Pearly |
| Streak | Yellow-white |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 5.93 - 6.14 |
| Density | 5.93 - 6.14 g/cm3 (Measured) |
| Birefringence | 0.005 - 0.007 |
Fluocerite-(Ce) was first described (without the Ce) in 1845 from hydrothermal veins in granite in Sweden.[4] Fluocerite-(La) was first described in 1969 from the type locality in central Kazakhstan.[3] The name tysonite was given in 1880 to the same type of mineral found in Colorado.[5][6] Tysonite-type structure is used for rare-earth fluorides with the P3c1 space group structure.[7]
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