Sturmanite - Encyclopedia

    Class : Sulphates, chromates, molybdates
    Subclass : Hydrated sulphates
    Crystal system : Rhombohedral
    Chemistry : Ca6Fe2(SO4)2[B(OH)4](OH)12 25H2O
    Rarity : Very rare


Sturmanite is an hydrated sulfate of the ettringite group, which forms prismatic hexagonal bipyramidal crystals of yellow to yellow-green color, rarely brown. It owes its name to B. Darko Sturman, Assistant Curator of the Royal Ontario Museum in Toronto, Canada. It is found in the oxidation zone of a manganese deposit. It is a mineral with a complex structure, [B(OH)4] groups partially substituting for SO4 groups. It is a very rare mineral sought after by the most informed collectors.

Sturmanite in the World

Sturmanite is found exclusively in the manganese mines of the Hotazel district in South Africa : exceptional crystals exceeding 30 cm come from the N'Chwaning II mine, those of Black Rock and Wessel having provided superb crystals, but of more modest dimensions (4 cm at most).

Sturmanite in France

This mineral is not present in the French underground.

Twinning

Twinning probable but not described.

Fakes and scams

No fake recorded for this species. It is a very difficult mineral to differentiate from ettringite without chemical analysis, some specimens of ettringite may be labeled sturmanite and vice versa. Some crystals may exhibit mixtures and be zoned with parts of ettringite composition and other sturmanite.



Hardness : 2.5
Density : 1,847
Fracture : Undeterminated
Streak : Brown to yellow




TP : Transparent to translucent
IR : 1.499 to 1.505
Birefringence : 0.002
Optical character : Uniaxial (+/-)
Pleochroism : Low
Fluorescence : None


Solubility : Insoluble

Magnetism : None
Radioactivity : None