ZWIESELITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous phosphates
    Crystal system : Monoclinic
    Chemistry : (Fe,Mn)2(PO4)F
    Rarity : Very rare

Zwieselite is a very rare primary phosphate of granitic pegmatites. It forms a series with triplite, its magnesium and calcium equivalent. Its name comes from its discovery location : Zwiesel (Germany). Zwieselite forms centimeter-sized cleavable masses of dark brown to cinnamon brown color, changing to yellowish brown in the presence of low calcium contents. The crystals are always very indistinct.

Main photo : Zwieselite from Sítio do Castelo Mine, Portugal © Pedro Alves

Zwieselite in the World

Zwieselite is best known from the phosphate pegmatites of Bavaria (Zwiesel, Hagendorf). It is found more anecdotally in those of the Czech Republic (Horni Slavkov), Portugal (Mangualde) and a few other localities.

Right photo : Zwieselite from Hagendorf, Bavaria, Germany © Vandall Thomas King


Zwieselite in France

In France, zwieselite is reported from the pegmatites of Limousin at Bessines-sur-Gartempe and Chanteloube (Haute-Vienne) and at Valmanya (Pyrénées-Orientales).

Twinning

No twinning known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 5 to 5.5
Density : 3.89 to 3.97
Fracture : Irregular to sub-conchoidal
Streak : Tan, white

TP : Translucent
RI : 1.686 to 1.713
Birefringence : 0.017
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None