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Empressite from Joe mine, Tombstone district
Category Telluride mineral
(repeating unit)
Strunz classification 2.CB.80
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pmnb
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 [1][2][3]

Empressite is a mineral form of silver telluride, AgTe. It is a rare, grey, orthorhombic mineral with which can form compact masses, rarely as bipyrimidal crystals.

Recent crystallographic analysis[4] 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,[5] 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.[3]


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