Fettelite
| Fettelite | |
|---|---|
|
Cluster of tiny fettelite crystals in a vug from Copiapó, Atacama Region, Chile - (size: 2x2 mm) | |
| General | |
| Category | Sulfosalt mineral |
| Formula (repeating unit) |
Ag16HgAs4S15 (rruff) or [Ag6As2S7]·[Ag10HgAs2S8] (mindat.org) |
| Strunz classification | 2.LA.30 |
| Crystal system | Monoclinic |
| Crystal class |
Sphenoidal (2) H-M symbol: (2) |
| Space group | C2 |
| Unit cell |
a = 15.00, c = 15.46 [Å] V = 3014 ų; Z = 8 |
| Identification | |
| Color | dark violet to red |
| Crystal habit | flakes, hexagonal, micaceous |
| Twinning | intimately twinned with six twin domains |
| Cleavage | perfect |
| Fracture | subconchoidal |
| Mohs scale hardness | 3.5 |
| Luster | metallic |
| Streak | dark vermillion |
| Diaphaneity | subopaque to opaque |
| Specific gravity | 6.29 |
| Optical properties | Biaxial, anisotrophism weak with strong red internal reflections |
| Refractive index | N(calc) = 1.74 |
| Birefringence | moderate white to brownish gray |
| References | [1][2] [3] |
Fettelite is a mercury-sulfosalt mineral with the chemical formula Ag16HgAs4S15. The mineral was first described by Wang and Paniagua (1996)[4] who named it after M. Fettel, a German field geologist who collected the first samples from Odenwald.[5] It was first collected in the Nieder-Beerbach mine, 10 km south of Darmstadt, Odenwald, Germany. Its normal occurrence is in hydrothermal veins, which can cut gabbro-diorite intrusives. It is closely related to other rare minerals like dervillite, daomanite, vaughanite and criddleite which are also found in the same type locality as fettelite.[3]
Fettelite occurs as clusters of hexagonal flakes. These flakes can get up to 0.2 mm across and around 5-10 µm thick. In more complex hexagonal tablets, somewhat larger sub parallel aggregates can be measured.[6] The birefringence of Fettelite is moderate white to grayish brown.[5]
References
- ↑ Mineralienatlas
- ↑ Mindat.org Accessed 4 November 2010
- 1 2 Jambor, John L.; Puziewicz, Jacek; Roberts, Andrew C. (1997). "New mineral name" (PDF). American Mineralogist. 82: 620–624.
- ↑ Wang, N. and Paniagua, A. (1996) Fettelite, a new Hg-sulfosalt mineral from Odenwald. Neues Jahrbuch für Mineralogie Monatshefte, 82, 313–320.
- 1 2 Bindi, Luca; Keutsch, Frank N.; Francis, Carl A.; Menchetti, Silvio (2009). "Fettelite, {Ag6As2S7}{Ag10HgAs2S8} from Chañarcillo, Chile: Crystal structure, pseudosymmetry, twinning, and revised chemical formula" (PDF). American Mineralogist. 94: 609–615. doi:10.2138/am.2009.3096.
- ↑ Mandarino, J.A (1997) Abstracts of new mineral description The Mineralogical Record, 28, 141-143.