Jacobsite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : MnFe2O4
    Rarity : Rare

Jacobsite belongs to the spinel group. It forms a continuous series with magnetite and can contain significant quantities of magnesium. It is an uncommon mineral from metamorphic manganese deposits. Its name comes from its place of discovery : the Jakobsberg mine (Sweden). Jacobsite rarely forms octahedral or cubic crystals of 2 cm or less and usually occurs in fine to coarse grained masses. It is exceptionally a manganese ore.

Main photo : 2 cm jacobsite from Nordmark Odal Field, Filipstad, Sweden © Joe Budd

Jacobsite of N'Chwaning II Mine, South Africa © Uwe Haubenreisser
Jacobsite of Jakobsberg Mine, Filipstad, Sweden © Molin Lee
Jacobsite from the Mendig pumice quarry, Germany © Christof Schäfer
Jacobsite of Iron Monarch Main Pit, Iron Knob, Australia © Douglas Merson

Jacobsite in the World

The Swedish deposits of Langban and Filipstad provided the world's best specimens of jacobsite, 2 cm cubes. The mines of N'Chwaning (South Africa) produced perfect octahedra almost centimeter in size. It is also reported in good samples at the Bald Knob mine, near Sparta, North Carolina.

Jacobsite in France

In France, jacobsite is reported at St-Jean-de-Maurienne (Savoie), on the island of Groix (Morbihan), at Gérardmer (Vosges) and at Tuc Usclat near Boutx (Haute-Garonne).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 6 to 6.5
Density : 4.75
Fracture : Irregular
Streak : Black to brown

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

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None

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