TETRADYMITE

    Class : Sulfides and sulfosalts
    Subclass : Tellurides
    Crystal system : Trigonal
    Chemistry : Bi2Te2S
    Rarity : Uncommon


Tetradymite is the most common telluride. It is a mineral that is found mainly in low to high temperature hydrothermal gold veins. It is associated with different tellurides (hessite, altaite, petzite), native bismuth and native gold. Its name comes from the Greek tetradumos (quadruple) in allusion to its twinned crystals. Tetradymite has a metallic luster and a steel gray color that tarnishes to grayish to iridescent. This mineral has a perfect cleavage that ensures a flow in flexible lamellae like molybdenite. Its crystals are rarely well formed : they are acute rhombohedra with striated faces, evoking hexagonal prisms, with frequent twins of 4 individuals. Tetradymite occurs more often in small foliated or lamellar masses. It is the main ore of tellurium and an accessory source of bismuth.


Main photo : Tetradymite and native gold from Jílové u Prahy, Czech Republic © Bohuslav Bures

Tetradymite in the World

The Zubkov (or Schubkau) gold deposit, near Banska Stiavnica (Slovakia) has produced the most beautiful crystals known: twinned individuals at most centimeters on altered trachyte matrix. The gold deposits of California (Carson Hill), and Colorado (Gold Hill) have also provided beautiful crystals. It is also known in Transylvanian deposits as Sacarimb and Moravite (Romania).

Right photo : Tetradymite from Pod Angleta, Banska, Slovakia © Martin Stevko

Tetradymite in France

In France, tetradymite is reported in different deposits but never in remarkable samples. It is described in the vicinity of Aurillac and St-Flour (Cantal), at the Chizeuil mine (Saône-et-Loire), in Tende (Alpes-Maritimes), etc...

Twinning

Twinning with 4 individuals on {01.8} and on {01.5} is known.

Fakes and treatments

No fakes listed for this mineral species.



Hardness : 1.5 to 2
Density : 7.3
Fracture : Undetermined
Streak : Light gray


TP : Opaque
RI : -
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None


Solubility : -

Magnetism : NoneRadioactivity : None