Gabrielite: Properties and Occurrences

Gabrielite is a rare thallium sulfosalt mineral with a chemical formula of Tl6Ag3Cu6(As, Sb)9S21 or Tl2AgCu2As3S7. It is a triclinic-pinacoidal black mineral containing antimony, arsenic, copper, silver, sulfur, and thallium. It was first reported in 2002 for its occurrence in the Lengenbach quarry, Binntal, Valais, Switzerland, and named after Walter Gabriel (born 1943), a Swiss mineral photographer. This region was transformed during the greenschist-garnet/amphibolite facies of metamorphism. Due to these many rare sulfosalts like gabrielite are found in this part of Switzerland.

General Information

  • Category: Sulfide mineral
  • Formula: Tl6Ag3Cu6(As, Sb)9S21
  • Crystal system: Triclinic
  • Crystal class: Pinacoidal (1) (same H-M symbol)

Fig: Gabrielite Рthallium sulfosalt mineral

Properties

  • Color: Grey to black
  • Crystal habit: Pseudo Hexagonal
  • Twinning: Common, with (100) as twin plane
  • Fracture: uneven
  • Mohs scale hardness: 1.5 – 2
  • Luster: Metallic
  • Streak: Blackish red
  • Diaphaneity: Opaque
  • Density: 5.38 g/cm3

Structure

Gabrielite has a pseudohexagonal shape and the crystal structure is composed of parallel sheets of ditriagonalization of hexagons which reduces it to a P3 symmetry. According to the American Mineralogist, Gabrielite shows a 6-Fold outline. Gabrielite is part of the triclinic crystal system, which means that the pseudohexagonal shape that this mineral occurs in nature with only has a center of symmetry.

Occurrence: A late-stage mineral in vugs in a hydrothermally-altered dolomitic marble.

Gabrielite is a sulfosalt mineral species occurring as idiomorphic crystals commonly found in cavities of a Triassic dolomitic rock. The physical properties of sulfosalts such as gabrielite, the mineral can be used for thermoelectric conducting, and magnetism.

Association: Hutchinsonite, hatchite, edenharterite, trechmannite, tennantite, realgar, rathite.

Distribution: From Lengenbach, Binntal, Canton Valais, Switzerland.

 

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