OTTRELITE

    Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Monoclinic
    Chemistry : (Mn,Fe,Mg)2Al4Si2O10(OH)4
    Rarity : Very rare

Ottrelite is an extremely rare silicate close to chloritoid. Initially confused with manganese chloritoid, ottrelite is now considered a separate species characterized by a greater number of manganese atoms than iron in its structural formula. It is found in cracks and cavities in weakly to moderately metamorphic rocks; it is also a medium temperature hydrothermal alteration mineral. It owes its name to its place of discovery : Ottrez (Belgium). Ottrelite forms flakes and pseudohexagonal scales of 4 mm at most, green to green-yellow, sometimes dark greenish gray.

Main photo : Ottrelite from Ottrez, Bihain, Wallonia, Belgium © Yannick Vessely

Ottrelite in the World

The "real" ottrelite is only known in the metamorphic massif of Stavelot, in the Belgian Ardennes, disseminated in schists and as a hydrothermal alteration mineral on the walls of a quartz vein. The other localities of ottrelite mentioned previously are in fact manganiferous chloritoids.

Ottrelite in France

Otavite is not present in the French underground.

Twinning

Polysynthetic twins are known parallel to [001].

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 6 to 7
Density : Undetermined
Fracture : Undetermined
Streak : Green to gray

TP : Translucent to transparent
RI : 1.709 to 1.732
Birefringence : 0.007
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : Sulfuric acid

Magnetism : NoneRadioactivity : None