MANSFIELDITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated arsenates
    Crystal system : Orthorhombic
    Chemistry : AlAsO4 2H2O
    Rarity : Rare to uncommon

Mansfieldite is an hydrated aluminum arsenate that forms a series with scorodite, a mineral with which it is frequently associated. Mansfieldite is a secondary mineral which appears to form by alteration of aluminous rocks mineralized with arsenic. It was named in honor of George Rogers Mansfield, a geologist with the US Geological Survey. Mansfieldite forms very small pseudo-octahedral crystals (2 mm at most) and usually occurs in fibrous spherolitic encrustations, up to 20 cm in diameter, and in porous cellular masses, also spherolitic, white to pale yellow-grey, sometimes bluish green or pink.

Main photo : Mansfieldite from Guanaco Mine, Taltal, Chile © Gianfranco Ciccolini

Mansfieldite from Guanaco Mine, Taltal, Chile© Pierre Clolus
Mansfieldite from Jote Mine, Atacama, Chile © Luigi Chiappino
Mansfieldite from Mount Cobalt Mine, Queensland, Australia © Judy Rowe
Mansfieldite from Cap Garonne, Var, France © Christophe Boutry

Mansfieldite in the World

Mansfieldite is known in association with scorodite at Djebel Debar (Algeria), and in quite a few German, American or Mexican metalliferous deposits.

Mansfieldite in France

In France, mainsfieldite is known in 1 mm crystals in the small copper mine of Cap Garonne (Var) as well as in Vaulry (Haute-Vienne).

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3.5 to 4
Density : 3.03
Fracture : Sub-conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.622 to 1.663
Birefringence : 0.020 to 0.032
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Acids

Magnetism : NoneRadioactivity : None