Florencite-(Sm)
Florencite-(Sm) is a very rare mineral of the plumbogummite group (alunite supergroup) with simplified formula SmAl3(PO4)2(OH)6. Samarium in florencite-(Sm) is substituted by other rare earth elements, mostly neodymium. It does not form separate crystals, but is found as zones in florencite-(Ce), which is cerium-dominant member of the plumbogummite group. Florencite-(Sm) is also a samarium-analogue of florencite-(La) (lanthanum-dominant) and waylandite (bismuth-dominant), both being aluminium-rich minerals.
| Florencite-(Sm) | |
|---|---|
| General | |
| Category | Phosphate mineral |
| Formula (repeating unit) | SmAl3(PO4)2(OH)6 |
| IMA symbol | Flo-Sm |
| Crystal system | Trigonal |
| Crystal class | Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) |
| Space group | R3m |
| Unit cell | a = 6.972, c = 16.182 [Å]; Z = 3 |
| Identification | |
| Color | Colorless, pale pink, pale yellow |
| Crystal habit | Sub-mm zones in florencite-(Ce) crystals |
| Cleavage | {0001}, distinct |
| Fracture | Uneven |
| Mohs scale hardness | 5.5-6 |
| Luster | Vitreous to greasy |
| Streak | White |
| Density | 3.6 (measured) |
| Optical properties | Uniaxal(+) |
| Refractive index | nω=1.70, nε=1.71 |
| References | |
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