Empressite is a
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...
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 has confirmed that empressite is a distinct mineral with orthorhombic crystal structure, different from the hexagonal Ag
5−xTe
3 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,
[Karakaya, I., Thompson, W.T.: J. Phase Equilibria 12, 56 (1991).] and therefore it is only
metastable
In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...
at ambient conditions. Given infinite time, it would phase separate into pure Ag
5Te
3 and pure Te.
The name empressite comes from the location of its discovery – the Empress Josephine mine,
Saguache County, Colorado
Saguache County (suh-WATCH ) is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 6,368. The county seat is Saguache.
History
Saguache County was formed December 29, 1866 in the Territory of Colorado w ...
, US. It was first described in 1914.
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References
Silver minerals
Telluride minerals
Orthorhombic minerals
Minerals in space group 62
Minerals described in 1914
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