ROSCOELITE

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Monoclinic
    Chemistry : KV2AlSi3O10(OH)2
    Rarity : Uncommon

Roscoelite is a vanadium mica, with a structure identical to that of muscovite with which it forms a continuous series, vanadium replacing aluminum in the octahedral sites. It is a hydrothermal mica formed in epithermal gold deposits where it accompanies native gold, fluorite and rhodochrosite. It is also found in the oxidation zone of uranium-vanadium deposits in sedimentary contexts. It was named in honor of Henry Enfield Roscoe, Professor of Chemistry at the University of Manchester. Roscoelite forms tiny crystals grouped in rosettes, scaly or flabelliform aggregates, or felt-like encrustations, dark brown to dark greenish brown in colour. It is one of the few vanadiferous minerals that resists weathering. It is locally an ore of vanadium.

Main photo : Roscoelite from Gambatesa Mine, Liguria, Italy © Gianluca Armellino

Roscoelite in the World

Roscoelite is found in the epithermal veins of Vatukoula (Fiji), Kalgoorlie (Australia) and Cripple Creek (Colorado). It is also abundant in the uranium and vanadium deposits of Uravan or Monument Valley (Colorado) where it is associated with the usual procession of secondary uranium and vanadium minerals (carnotite, tyuyamunite).

Roscoelite in France

In France, roscoelite is reported in Saint-Martin-de-Belleville (Savoie).

Twinning

No known twinning for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2.5
Density : 2.92 to 2.94
Fracture : Micaceous
Streak : White

TP : Translucent to transparent
RI : 1.590 to 1.704
Birefringence : 0.050 to 0.094
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None