Empressite
Empressite is a mineral form of silver telluride, AgTe. It is a rare, grey, orthorhombic mineral with which can form compact masses, rarely as bipyramidal crystals.
| Empressite | |
|---|---|
 Empressite from Joe mine, Tombstone district | |
| General | |
| Category | Telluride mineral |
| Formula (repeating unit) | AgTe |
| IMA symbol | Eps[1] |
| Strunz classification | 2.CB.80 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pmnb |
| Identification | |
| Color | Pale bronze |
| Crystal habit | Granular masses |
| Cleavage | None |
| Fracture | Uneven to subconchoidal |
| Tenacity | Brittle |
| Mohs scale hardness | 3.5 |
| Luster | Metallic |
| Streak | Gray-black to black |
| Diaphaneity | Opaque |
| Specific gravity | 7.6 |
| Optical properties | Opaque |
| Pleochroism | Very strong, in gray to creamy white |
| References | [2][3][4] |
Recent crystallographic analysis[5] has confirmed that empressite is a distinct mineral with orthorhombic crystal structure, different from the hexagonal Ag5−xTe3 with which empressite has been commonly confused in mineralogy literature. At the same time, empressite does not appear on the equilibrium Ag-Te phase diagram,[6] and therefore it is only metastable at ambient conditions. Given infinite time, it would phase separate into pure Ag5Te3 and pure Te.
The name empressite comes from the location of its discovery – the Empress Josephine mine, Saguache County, Colorado, US. It was first described in 1914.[4]
References
- Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- http://rruff.geo.arizona.edu/doclib/hom/empressite.pdf Handbook of Mineralogy
- http://www.webmineral.com/data/Empressite.shtml Webmineral
- http://www.mindat.org/min-1379.html Mindat
- L. Bindi et al., American Mineralogist, 89, 1043 (2004)
- Karakaya, I., Thompson, W.T.: J. Phase Equilibria 12, 56 (1991).