DICKITE

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Monoclinic
    Chemistry : Al2Si2O5(OH)4
    Rarity : Quite common


Dickite is a phyllosilicate, polymorph of nacrite and kaolinite, belonging to the kaolinite-serpentine group. Its certain occurrences are quite frequent, but dickite is probably much more abundant than its number of deposits suggests, its rigorous identification requiring significant analytical resources. It is a mineral mainly of hydrothermal origin, which forms by alteration at low temperature of aluminous minerals, in particular feldspars, around hydrothermal veins and within them. It was named in honor of the chemist and metallurgist Allan Brugh Dick. Dickite is transparent to translucent in crystals, opaque in mass. It appears in lamellar aggregates or in compact white masses, sometimes yellowish-green, with a smooth feel, made up of microscopic crystals. The visible crystals are rare, forming pseudohexagonal lamellae of 4 mm at most, sometimes grouped in sheaves or radiated aggregates. It offers the same wide range of uses as kaolinite : ceramics, papermaking, rubber industry, ion exchange material, saponifiers, degreasers, but the rarity of large deposits results in fairly marginal use.

Main photo : Dickite from Mas Lavayre, Lodève, Hérault, France © Oliver Dziallas

Dickite from Mas Lavayre, Lodève, Hérault, France © Elmar Lackner
Dickite on quartz from Saint-Clair, Pennsylvania, USA © Harold Moritz
Dickite from Buick Mine, Missourri, USA © Steve Stuart
Dickite from Mas d’Alary, Hérault, France © Matteo Chinellato

Dickite in the World

Among the deposits of this mineral, we can note the large white masses of pure dickite existing at Clairwood, near Lamontville (South Africa), at Schuylkill and at Saint-Clair (Pennsylvania). Dickite is present in many American deposits : Bisbee (Arizona), Red Mountain (Colorado), etc...

Dickite in France

In France, 4 mm crystals (perhaps the largest known) were discovered in the hydrothermal alteration zone of the Rabejac and Mas d'Alary uranium deposits (Hérault). It is also reported at Cap Garonne (Var), at the Bois-de-la-Roche quarry (Loire-Atlantique), at Oms and Fontcouverte (Pyrénées-Orientales) and in the Alps at St-Jean-de-Maurienne (Savoie) as well as at the Champa quarry near Grenoble (Isère).

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.



Hardness : 2 to 2.5
Density : 2.60
Fracture : Micaceous
Streak : White


TP : Transparent
RI : 1.561 to 1.570
Birefringence : 0.005 to 0.006
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None


Solubility : Insoluble


Magnetism : None
Radioactivity : None

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