| Fluocerite-(La) | |
| Formula: | (La,Ce)F3 |
| Molweight: | 196.02 |
| Strunz: | 03.AC.15 (03) |
| Dana: | 09.03.04.02 (09) |
| System: | Trigonal |
| Class: | Hexagonal scalenohedral |
| Symmetry: | Pc1 (No. 165) |
| Unit Cell: | 328.80 ų (Calculated from Unit Cell) |
| Colour: | Greenish-yellow |
| Habit: | Platy, tabular |
| Cleavage: | Indistinct, Imperfect |
| Mohs: | 4-5 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Transparent to translucent |
| Density: | 5.93 |
| Birefringence: | 0.006 |
| Fluocerite-(Ce) | |
| Formula: | (La,Ce)F3 |
| Molweight: | 196.99 |
| Strunz: | 3/A.10-20 |
| Dana: | 9.3.4.1 |
| System: | Trigonal |
| Class: | Hexagonal Scalenohedral |
| Unit Cell: | 320.86 ų (Calculated from Unit Cell) |
| Colour: | Light yellow; darkening to yellow- and red-brown; colourless to pale pink (transmitted light) |
| Habit: | Massive, Primsatic |
| Cleavage: | Distinct/Good |
| Fracture: | Irregular/Uneven, Splintery, Sub-Conchoidal |
| Tenacity: | Brittle |
| Mohs: | 4.5-5 |
| Luster: | Vitreous, Resinous, Pearly |
| Streak: | Yellow-white |
| Diaphaneity: | Transparent to translucent |
| Gravity: | 5.93 - 6.14 |
| Density: | 5.93 - 6.14 g/cm3 (Measured) |
| Birefringence: | 0.005 - 0.007 |
Fluocerite, also known as tysonite, is a mineral consisting of cerium and lanthanum fluorides, with the chemical formula .[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-(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. 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]