Gabrielite


Gabrielite is a rare thallium sulfosalt mineral with a chemical formula of Tl6Ag3Cu69S21 or Tl2AgCu2As3S7.
It was first reported in 2002 for its occurrence in the Lengenbach quarry, Binntal, Valais, Switzerland, and named after Walter Gabriel, a Swiss mineral photographer.
This region was transformed during the greenschist-garnet/amphibolite facies of metamorphism. Due to this many rare sulfosalts like gabrielite are found in this part of Switzerland.

Structure and properties

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.
Looking into the optical mineralogy of this mineral we have to define if the mineral is isotropic, or anisotropic. According to Mindat.org, Gabrielite has anisotropic properties. Which means that the velocity of light changes in crystallographic direction, this is easily identifiable in thin section. Another optical property is birefringence. Gabrielite has very weak anisotropism which is the reason why gabrielite shows little to no birefringence. Mindat.org stated that the mineral gabrielite is not pleochroic.
Gabrielite is a sulfosalt mineral species occurring as idiomorphic crystals commonly found in cavities of Triassic dolomite. The physical properties of sulfosalts such as gabrielite, the mineral can be used for thermoelectric conducting, and magnetism.