TILASITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous arsenates
    Crystal system : Monoclinic
    Chemistry : CaMg(AsO4)F
    Rarity : Rare to uncommon

Tilasite is a fairly rare arsenate, typical of metamorphic deposits of manganese or zinc containing arsenic. Tilasite is associated with many manganese minerals, as well as calcite and barite. It was named in honor of the Swedish mining engineer Daniel Tilas. It occurs in equant or elongated crystals, often complex, up to 3.5 cm. They form subparallel aggregates, veinlets or masses. Its color is variable : usually milky white, it can become gray to purplish gray, pink or apple green to olive green.

Main photo : Tilasite from Wanni Glacier, Valais, Switzerland © Stephan Wolfsried

Tilasite from Fuchs Quarry, Bavaria, Germany © Christophe Boutry
Tilasite from Monte Cervandone, Piemond, Italy © Enrico Bonacina
Tilasite from Falotta, Grisons, Switzerland © Stephan Wolfsried
Tilasite from Falotta, Grisons, Switzerland © Stephan Wolfsried

Tilasite in the World

Tilasite is present in numerous metamorphic manganese deposits in India (Jhabua), Sweden (Langban), and in the metamorphic zinc deposits of Sterling Hill (New Jersey), Bisbee (Arizona), Beltana (Australia), etc... Tilasite is found more curiously at Mount Cherbadung near Binn (Switzerland).

Tilasite in France

Tilasite is not present in the French underground.

Twinning

Twinning is known on {001}.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 5
Density : 3.77
Fracture : Undetermined
Streak : White

TP : Translucent
RI : 1.640 to 1.675
Birefringence : 0.035
Optical character : Biaxial -
Pleochroism : None
Fluorescence : Yellow, orange, red

Solubility : Nitric acid, hydrochloric acid

Magnetism : NoneRadioactivity : None