Braunite - Encyclopedia

    Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Tetragonal
    Chemistry : Mn7SiO12
    Rarity : Common


Braunite is a notable component of large sedimentary manganese deposits (India, South Africa, etc.), especially abundant when they have undergone slight metamorphism. It is associated with a procession of manganese oxides and hydroxides (manganite, pyrolusite, psilomelane). This manganese silicate is also found in manganiferous contact deposits and in hydrothermal veins. It owes its name to Kammerrath Braun who provided the type sample. Braunite forms small, almost regular octahedra, exceptionally reaching 5 cm, often with striated truncations. In manganese deposits, it more often occurs in grainy masses made up of myriads of microscopic patches. It is a dark, brownish-black to steel-grey mineral with a strong metallic luster. It is an important manganese ore.


Main photo : Braunite on amphibole from Caspar Quarry, Ettringen, Germany © Volker Betz

Braunite from N'Chwanning II Mine, Kuruma, South Africa © Gianfranco Ciccolini
Braunite from St-Marcel, Aosta Valley, Italy © Enrico Bonacina
Braunite from Gambatesa Mine, Liguria, Italy © Stephan Wolfsried
Twinned braunite from St-Marcel, Aosta Valley, Italy © Ortenzi Andrea (SEM picture)

Braunite in the World

Very beautiful crystals come from the large Indian manganese deposits of Nagpur and Tirodi, as well as the Swedish metamorphic deposit of Langban. The mines of the large manganiferous district of Hotazel (South Africa), in particular that of Black Rock, gave superb brilliant crystals which can reach 2 cm. in Europe, the manganese deposit of St-Marcel (Valley of Aosta, Italy) has also yielded beautiful crystals associated with piemontite.

Braunite in France

In France, braunite is known incidentally in the small metamorphic manganese deposits of the Vosges, Haut-Poirot and Dambach-la-Ville.

Twinning

twin is known on {112}, producing a small re-entrant angle on {011}.

Fakes and treatments

No fake inventories for this mineral species.



Hardness : 6 to 6.5
Density : 4.72 to 4.83
Fracture : Irregular
Trace : Brown-black, gray



TP : Opaque
RI : -
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None


Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None

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