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 bipyrimidal crystals. It is a rare hexagonal mineral form of silver telluride.

The name empressite comes from the location of its discovery – the Empress Josephine mine, Saguache County, Colorado, US. It was first described in 1914.

General Information

  • Category: Telluride mineral
  • Formula: AgTe
  • Crystal system: Orthorhombic
  • Crystal class: Dipyramidal (mmm)

Properties

  • Color: Pale bronze
  • Crystal habit: Granular masses
  • 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

Recent crystallographic analysis 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, and therefore it is only metastable at ambient conditions. Given infinite time, it would phase separate into pure Ag5Te3 and pure Te.

 

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