GLAUCONITE

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Monoclinic
    Chemistry : (K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2
    Rarity : Common

Glauconite is a mineral close to the micas group to which it is sometimes attached, but its precise definition is complex and poorly defined. Some authors consider it to be a variety of celadonite. It is a biotite alteration mineral that forms in shallow marine environments under reducing conditions. Its name comes from the Greek glaukos (green-blue) because of its color. Glauconite occurs in small flattened pseudohexagonal crystals, yellowish green to blue-green in color, resembling chlorite, stacked on top of each other to form small, finely grained rounded clusters. Thanks to its high potassium content (4 to 9.5% K2O), glauconite is used in agriculture for soil amendment. It also has little use in the field of green pigments, and once played a role as an ion exchanger.


Main photo : Glauconite from the alluvium of the Loire, France © François Périnet

Glauconite in the World

A common mineral, glauconite is particularly abundant in Alabama, New Zealand and Great Britain.

Glauconite in France

In France, glauconite is known in Villers-sur-Mer (Calvados), in the alluvium of the Loire, in certain heavy sands of Finistère and Morbihan, etc...

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 2
Density : Underterminated
Fracture : Micaceous
Streak : Green

TP : Translucent to opaque
RI : -
Birefringence : -
Optical character : -
Pleochroism : None
Fluorescence : None

Solubility : Insoluble


Magnetism : Paramagnetic
Radioactivity : None