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 Ag5βˆ’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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