Beidellite - Encyclopedia

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal System : Monoclinic
    Chemistry : (Ca0.5,Na)0.3Al2(Si,Al)4O10(OH)2 nH2O
    Rarity : Common

Beidellite is a hydrated phyllosilicate from the smectite group. It is a naturally white clay which is most often colored pink to brownish, or grey-pink ; it presents itself like most clays in earthy, compact and unctuous masses. It owes its name to its place of discovery : Beidell (Colorado, USA). Beidellite is a silicate weathering mineral that typically forms through the weathering of basic and ultrabasic igneous rocks, but can also result from the hydrothermal weathering of plagioclases in hydrothermal deposits, including copper-bearing porphyries. Beidellite is, along with montmorillonite and saponite, one of the main constituents of bentonite.

Main photo : Beidellite from Cameron, Arizona, USA © Chris Emproto

Beidellite in the World

Widespread worldwide in loess, soils and superficial alterites, beidellite never forms macroscopic crystals or specimens of aesthetic value.

Beidellite in France

In France, as everywhere in the world, beidellite is very present.

Twinning and special crystallizations

No known twin for this mineral species.

Fakes and treatments

No fake or treatments identified for this mineral species, but difficult to identify without heavy laboratory equipment.

Hardness : 1 to 2
Density : 2 to 3
Fracture : Irregular
Trace : White

TP : Translucent
RI : 1.494 to 1.533
Birefringence : 0.032
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None

Solubility : Insoluble

Magnetism : None
Radioactivity : None


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