ROCKBRIDGEITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous phosphates
    Crystal system : Orthorhombic
    Chemistry : MnFe4(PO4)3(OH)5
    Rarity : Fairly common

Rockbridgeite is a manganese and iron phosphate that forms a series with frondelite, the manganese pole. It is a secondary phosphate resulting from the alteration of primary phosphates (triphylite in particular) in granitic pegmatites, sometimes present in limonitic iron deposits. It owes its name to its discovery location ; Rockbridge County in Virginia (USA). Rockbridgeite is rare in fibrous crystals, reaching 3 cm at most, and occurs mainly in botryoidal masses and incrustations with fibrous or radiate texture, and in sheaves. It is dark olive green to greenish-black in color, turning reddish-brown through surface oxidation.

Main photo : Rockbridgeite from Fletcher Mine, New Hampshire, USA © David Busha

Rockbridgeite from Tip-Top Mine, South Dakota, USA © Jeff Weissman
Rockbridgeite from Hagendorf Pegmatites, Germany © Stephan Wolfsried
Rockbridgeite from Hagendorf Pegmatites, Germany © Volker Betz
Rockbridgeite from Clara Mine, Germany © Michael Förch

Rockbridgeite in the World

Rockbridgeite is a fairly common mineral, known from most classic pegmatite districts in phosphates : Hagendorf (Germany), Tip-Top, Etta, Bull Moose and Fletcher (USA), Galileia district (Minas Gerais, Brazil), etc...

Rockbridgeite in France

In France, rockbridgeite is reported in the Vilate pegmatite near Chanteloube (Haute-Vienne). It is also known at La Fumade (Tarn) and in the Collioure pegmatites (Pyrénées-Orientales).

Twinning

No twinning known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 3.5 to 4.5
Density : 3.45 to 3.6
Fracture : Irregular
Streak : Gray-green to pale brown

TP : Translucent to opaque
RI : 1.873 to 1.897
Birefringence : 0.022
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None