DANNEMORITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Monoclinic
    Chemistry : Mn2(Fe,Mg)5Si8O22(OH)2
    Rarity : Rare

Dannemorite (recently renamed clino-ferro-suenoite) belongs to the group of monoclinic amphiboles. It is a rare manganiferous amphibole, which forms a series with tirodite, which is found in metamorphosed manganiferous rocks and formations poor in iron. Its name is taken from its locality of discovery : Dannemora (Sweden). Dannemorite occurs in prismatic to fibrous crystals no larger than 1 cm, dark brownish green or greenish gray in color.

Main photo : Dannemorite from Stollberg orefield, Väster Silvberg, Smedjebacken, Dalarna County, Sweden © Vandall King

Dannemorite in the World

Dannemorite is well represented in Sweden, where it has been described : Dannemora, Nävekvarn, Brunsjö... It is also known in several other localities, notably in Broken Hill (Australia), in Guarulhos (Sao Paulo, Brazil) and in Japan.

Dannemorite in France

In France, dannemorite forms small crystals in the Haute-Maurienne valley (Savoie).

Twinning

Twins are known and parallel to {100}.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 5 to 6
Density : 3.1 to 3.6
Fracture : Irregular
Streak : White

TP : Opaque to transparent
RI : 1.639 to 1.708
Birefringence : 0.025 to 0.037
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : Insoluble


Magnetism : None
Radioactivity : None