Empressite

Empressite is a mineral form of silver telluride, AgTe. It is a rare, grey, hexagonal crystal with which can form aggregates of bipyrimidal crystals. Twins do not form. Density 7600 kg.m^-3.

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Recent crystallographic analysis ^[1] has confirmed that empressite is a distinct mineral with orthorhombic crystal structure, different from the hexagonal Ag_5-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 ^[2], 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, USA.

References

1. ^ L. Bindi et al., American Mineralogist, 89, 1043 (2004)
2. ^ Karakaya, I., Thompson, W.T.: J. Phase Equilibria 12, 56 (1991).