MANGANITE

    Class : Oxides and hydroxides
    Subclass : Hydroxides and hydrates
    Crystal system : Monoclinic
    Chemistry : MnO(OH)
    Rarity : Common


Formerly called "acerdese", manganite is the most common manganese hydroxide. It is found mainly in low-temperature hydrothermal deposits, as well as in sedimentary manganese deposits (Nikopol, Ukraine). Manganite easily loses its water and readily pyrolusite pseudomorphs, sometimes psilomelane and hausmannite ; this easy dehydration explains its rarity in outcrops in favor of pyrolusite, stable in surface conditions. It owes its name to its chemical composition. Manganite has a submetallic luster and is dark steel gray to iron black in color, manganite has perfect cleavage and forms short to elongated prismatic crystals, with striated prism faces, united in fibrous aggregates, sometimes radiated or acicular. The concretionary and collomorphic varieties, probably deriving from psilomelane, are common and constitute grainy masses with a more or less fibrous texture. Manganite is an essential constituent of large manganese deposits and therefore a major ore of this metal.

Main photo : Manganite from Ilfeld, Harz, Germany © Dan Weinrich

Manganite from Ilfeld, Harz, Germany © Oleg Lopatkin
Manganite from N'Chwaning Mine, South Africa © Gianfranco Ciccolini
Twinned manganite from Ilfeld, Harz, Germany © Ko Jansen
Manganite from Haut-Poirot, Vosges, France © Alain Tuel

Manganite in the World

The most beautiful specimens of manganite are sheaves of prismatic crystals which reach 10 cm associated with calcite and barite, they were produced by the Ilfeld mine (Harz, Germany). Similar but smaller radiated showers (2 cm crystals) are reported in South Africa (N'Chwaning Mine). Well-formed centimeter-sized crystals come from the sedimentary iron-manganese mines of Michigan (Jackson and Marquette mines), as well as the Akikoken mine (Ontario, Canada).

Manganite in France

In France, the small manganese deposits of Adervielle (Hautes-Pyrénées) and Haut-Poirot (Vosges) have produced prismatic or acicular manganite crystals reaching 5 and 10 mm respectively (exceptionally 5 cm). It is also known at the Rivet quarry near Peyrebrune (Tarn) and has also been reported in many small deposits.

Twinning

Twins are known on {011} and on {100} by contact and by interpenetration.

Fakes and treatments

No fakes recorded for this mineral species.



Hardness : 4
Density : 4.29 to 4.34
Fracture : Splintery
Streak : Red-brown to black


TP : Opaque
RI : 2,250 to 2,530
Birefringence : 0.028
Optical character : Biaxial +
Pleochroism : Low
Fluorescence : None


Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None