GAUDEFROYITE

    Class : Carbonates, nitrates, borates
    Subclass : Borates
    Crystal system : Hexagonal
    Chemistry : Ca4Mn3(BO3)3(CO3)(O,OH)3
    Rarity : Very rare

Gaudrefroyite is a complex borate of calcium and manganese, whose structure includes CO3 groups. It is a very rare mineral present in some manganese deposits, particularly in limestone environments. It was named in honor of Abbe Christophe Gaudefroy, a French mineralogist who was particularly interested in the minerals of Morocco. Gaudefroyite occurs in acicular crystals or stubby prisms of purplish-blackish brown to black color. It is an occasional manganese ore.

Main photo : 1.8 cm gaudefroyite from N'Chwaning II Mine, South Africa © Jordi Fabre

3 cm gaudefroyite from Tachgagalt Mine, Morocco © Vincent & Michele Gallo 
Gaudefroyite and andratite from N'Chwaning II Mine, South Africa © Jordi Fabre
Gaudefroyite and andratite from N'Chwaning II Mine, South Africa © Tony Peterson
Acicular gaudefroyite from Caspar Quarry, Ettringen, Germany © Christof Schäfer

Gaudefroyite in the World

Magnificent bundles of blackish purplish-brown gaudefroyite needles, exceeding 5 cm, were encountered at the Tachgagalt mine, near Ouarzazate (Morocco). Manganese mines in the Hotazel district of South Africa (N'Chwaning, Wessel) also produce superb crystals up to 5 cm by 1.5 cm. Gaudefroyite is also known in millimeter crystals at the Caspar quarry near Ettringen in Germany.

Gaudefroyite in France

Gaudefroyite is not present in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 6
Density : 3.35 to 3.50
Fracture : Conchoidal
Streak : Brown

TP : Opaque
RI : 1.805 to 2.020
Birefringence : 0.210
Optical character : Uniaxial +
Pleochroism : Strong
Fluorescence : None

Solubility : -


Magnetism : None
Radioactivity : None