CANCRINITE

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Hexagonal
    Chemistry : Na6Ca2Al6Si6O24(CO3)2
    Rarity : Uncommon

Cancrinite is a mineral typical of alkaline rocks (nepheline syenites and their pegmatites, ijolites, etc...), in which it can have a primary or secondary origin, by alteration of nepheline. Formerly designating a group, this name is now restricted to carbonate terms, chlorinated terms being called davyne. It was named in honor of Count Egor Frantsevich Kankrin, Russian Minister of Finance. Usually massive, cancrinite is rarely hexagonal prismatic crystals, ending in a flattened pyramid, which does not exceed 2 cm. Its color is variable: colorless, honey yellow, gray, green, blue to gray-blue, reddish. Easily altered, cancrinite transforms into a mixture of zeolite, carbonate and kaolinite.


Main photo: Cancrinite from Caspar Quarry, Ettringen, Germany © Stephan Wolfsried

Cancrinite in the World

Beautiful masses associated with sodalite come from Bancroft (Canada) and Miass, in the Ilmen Mountains (Urals, Russia), as well as nepheline syenites from Gabon (Mabounié) where they are a beautiful honey color studded with biotite. Litchfield (Maine) produced very aesthetic decimetric clusters of cancrinite mixed with blue sodalite. Cancrinite is common in the nepheline syenites of Lovozero (Kola, Russia) and Mont St-Hilaire (Canada). It is also present in the lavas of Laacher (Eifel, Germany) and Vesuvius (Italy).

Right photo : Blue cancrinite from Farneze, Lazio, Italy © Di Domenico Dario

Cancrinite in France

Cancrinite is only found in France in French Polynesia on the island of Tahiti and Raiatea.

Twinning

Twins are rare and lamellar.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 5-6
Density : 2.4 to 2.5
Fracture : Irregular
Streak : White

TP : Transparent to translucent
RI : 1.495 to 1.528
Birefringence : 0.012 to 0.025
Optical character : Uniaxial +/-
Pleochroism : Low
Fluorescence : None

Solubility : Acids


Magnetism : None
Radioactivity : None

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