Cervandonite
Cervandonite is a rare arsenosilicate mineral. It has a chemical formula (Ce,Nd,La)(Fe3+
,Fe2+
,Ti4+
,Al)
3SiAs(Si,As)O
13 or (Ce,Nd,La)(Fe3+
,Fe2+
,Ti,Al)
3O
2(Si
2O
7)(As3+
O
3)(OH). It has a monoclinic crustal structure with supercell (Z=6), the crystal structure was established as a trigonal subcell, with space group R3m and a = 6.508(1)Ǻ, c = 18.520(3) Ǻ, V 679.4(2) Ǻ3, and Z=3. It was first described by Buhler Armbruster in 1988, but it has proven to be problem due to the extreme scarcity of single crystals and its unusual replacement of silicon and arsenic. Cervandonite is named after the location where it was first described, Pizzo Cervandone (Scherbadung), Italy in the Central Alps.
| Cervandonite | |
|---|---|
Cervandonite is a classic and very sought after mineral from Binntal. | |
| General | |
| Category | Silicate mineral |
| Formula (repeating unit) | (Ce,Nd,La)(Fe3+ ,Fe2+ ,Ti,Al) 3O 2(Si 2O 7)(As3+ O 3)(OH) |
| Strunz classification | 9.BE.09.2 |
| Crystal system | Trigonal |
| Space group | R3m |
| Identification | |
| Color | Black |
| Crystal habit | Aggregates and rosettes of tabular crystals |
| Cleavage | {001} Indistinct |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Luster | Adamantine |
| Streak | Brownish black |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 4.9 (calculated) |
| Optical properties | Biaxial |
| Refractive index | nα = 1.990 nγ = 2.000 |
| Pleochroism | Yellowish, reddish brown to black |
| References | |
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