BRANNERITE

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Monoclinic
    Chemistry : (U,Ca,Y,Ce)(Ti,Fe)2O6
    Rarity : Uncommon

Brannerite is a mineral discovered in the Idaho placers. Uranium is strongly oxidized there in the form of U6+, and frequently replaced by calcium (more than 3% of CaO), thorium (13% of ThO2), cerium (7% of Ce2O3), and yttrium (6.5% Y2O3). Its name was given to it in honor of Casper Branner, professor of geology and president of Stanford University. It is found in granitic pegmatites and in certain hydrothermal veins as well as in the alluvial deposits associated with them (Blind River, Ontario, Canada). It is a frequently metamict mineral of variable hue, black to yellow-brown, sometimes black-greenish or yellow-orange. The crystals are elongated, orthorhombic, often flattened on {010}. It sometimes constitutes a uranium ore, especially in alluvium.

Main photo : Brannerite from Power Station, Sportgastein, Austria © Stephan Wolfsried

Brannerite in the World

Potassic granitic pegmatites provided the largest crystals : metamict individuals up to 30 cm weighing several kilos (Fuente Ovejuna and Hornachuelos, Andalusia, Spain) or large yellow-orange crystals (Australian deposit of Crocker's Well). In these pegmatitic deposits, brannerite is associated with uraninite and ilmenite. Brannerite is also known in hydrothermal veins where it occurs in black needles of barely 1 cm, striated according to the elongation as in the gold and uranium cracks of the cobalt deposit of Bou-Azzer (Morocco).

Brannerite in France

In France, the auriferous veins of La Gardette (Isère) and the copper-molybdenum deposit of Château-Lambert (Haute-Saône) have produced centimetric needles, associated with native gold and uraninite.

Photo on the right : Brannerite and native gold from La Gardette, Isère, France © Yannick Vessely

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake inventories for this mineral species.


Hardness : 4.5 to 5.5
Density : 4.2 to 5.4
Fracture : Conchoidal
Trace : Brown-yellow to brown-green

TP : Opaque
RI : 2.23 to 2.3
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None

Solubility : Sulfuric acid

Magnetism : None
Radioactivity : Strong

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