Groutite - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Hydroxides
    Crystal system : Orthorhombic
    Chemistry : Mn3+O(OH)
    Rarity : Rare

Groutite is an oxide of manganese that is part of the diaspore group. It is the trimorph of manganite and feitknechtite. It forms in altered BIFs, in manganese deposits that have undergone metamorphism, and in hydrothermal environments. It was named in honor of Frank Fitch Grout, a petrologist from the University of Minnesota (USA). It is in the form of shiny black crystals grouped in barrels or rosettes, botryoidal masses, needles or millimetric prisms. It is an accessory manganese ore.

Groutite in the World

The most beautiful specimens are centimetric rosettes from Zavalye graphite field (Ukraine) and from South African manganese deposits (Hotazel and N'Chwaning Mines). Decimetric botryoidal masses are from Mahnomen pit, Minnesota, the type locality.

Groutite in France

In France, groutite is reported in Saphoz (Haute-Saône) and on the Plateau d'Ambulla (Pyrénées-Orientales).


Twins are reported, but not studied.

Fakes and treatments

No fake recorded for this mineral species. Can sometimes be confused with the manganite with which it shares its deposits.

Hardness : 3.5 to 4
Density : 4.144
Fracture : Urregular
Trace : Dark brown

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

Solubility : Hydrochloric acids

Magnetism : None
Radioactivity : None