Disthene (or Kyanite, or Cyanite)

Group of alumina silicates - Nesosubsilicates

Formule chimique : Al2SiO5
Système cristallin : Triclinic
Etymologie : From Greek di: two, and from stenos: strength. From its blue color for cyanite.
Dureté : 7.5 along the elongation and 4.5 perpendicularly.
Densité : 3.6 – 3.7
Propriétés physiques : Vitreous to pearly luster. White to blue color. Transparent to translucent. Cracked fracture. Perfect cleavage (100).
Propriétés chimiques : Insoluble in acids.
Formule chimique : Al2SiO5
Habitus : In aggregate of lamellar crystals.
Gîtologie : Disthene is a mineral of medium to high pressure, low to medium temperature aluminous metamorphic rocks and quartz and pegmatite veins. Polymorph of sillimanite and andalusite.
Determination : Easy because of its blue color and its habitus in lamellar crystals.
Utilisation : Disthene can be used to manufacture ceramics with thermal and chemical resistance (acid resistance). When it is of gem quality, kyanite is used in jewelry.

The kyanite is found in micaschists, gneiss and pegmatites. It is known in France in the Armorican Massif (Mont d’Arrée, Evel valley, Baud, Bouvron, Fay), in the Massif Central (Mont Pilat, St Etienne, St Chamond), in the Massif des Maures.
Beautiful specimens come from the Swiss and Austrian Alps.

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