RANCIEITE

    Class : Oxides and hydroxides
    Subclass : Hydroxides and hydrates
    Crystal system : Hexagonal
    Chemistry : CaMn4O9 3H2O
    Rarity : Rare

Rancieite belongs to the psilomelane group, which includes manganese oxides of colloidal origin that usually evolve into better crystallized products. Like most minerals in the psilomelane group, it is a mineral of the surface oxidation zones of manganese deposits. It also forms in hydrothermal deposits at the expense of primary manganese minerals. It owes its name to its discovery location : Rancié near Vicdessos (Ariège). Rancieite is a rare mineral, frequently associated with goethite, and which essentially forms polycrystalline aggregates, stalactites and dark gray to black incrustations.

Main photo : Rancieite on ankerite from St Nicolas Mine, Steinbach, Haut-Rhin, France © Thierry Brunsperger

Rancieite in the World

Rancieite is known in the superficial parts of American (Ajo, Batesville, etc...), German (Winterberg, Harz), and English (Newbiggin, Durham) deposits.



Rancieite in France

The most beautiful samples of rancieite known include radiated groups in limonite geodes from the definition site: Rancié, near Vicdessos in the Pyrenees (Ariège). It is also known in Saphoz (Haute-Saône), Ste-Marie-aux-Mines (Haut-Rhin), Batère (Pyrénées-Orientales), Peyrebrune (Tarn), etc...

Right photo : Rancieite on ankerite from St Nicolas Mine, Steinbach, Haut-Rhin, France © Thierry Brunsperger

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2.5 to 3
Density : 3.20
Fracture : Undetermined
Streak : Dark brown

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

Solubility : -

Magnetism : NoneRadioactivity : None