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Empressite

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Empressite
Empressite from Joe mine, Tombstone district
General
CategoryTelluride mineral
Formula
(repeating unit)
AgTe
IMA symbolEps[1]
Strunz classification2.CB.80
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPmnb
Identification
ColorPale bronze
Crystal habitGranular masses
CleavageNone
FractureUneven to subconchoidal
TenacityBrittle
Mohs scale hardness3.5
LusterMetallic
StreakGray-black to black
DiaphaneityOpaque
Specific gravity7.6
Optical propertiesOpaque
PleochroismVery strong, in gray to creamy white
References[2][3][4]

Empressite or tellursilberblende 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.

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

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  1. ^ 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.
  2. ^ http://rruff.geo.arizona.edu/doclib/hom/empressite.pdf Handbook of Mineralogy
  3. ^ http://www.webmineral.com/data/Empressite.shtml Webmineral
  4. ^ a b http://www.mindat.org/min-1379.html Mindat
  5. ^ L. Bindi et al., American Mineralogist, 89, 1043 (2004)
  6. ^ Karakaya, I., Thompson, W.T.: J. Phase Equilibria 12, 56 (1991).