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Download hereGENERAL DESCRIPTION
Kyanite (called in the past disthène) is an aluminosilicate. It is formed in metamorphic rocks having undergone high pressures (micaschists, gneisses). It is seldomly associated to other minerals showing the same chemical composition but different structure (sillimanite and andalusite). These three species are thus said "polymorphic" of this aluminosilicate composition. Each of these three minerals form under different conditions of pressure and temperature.
In theory, these three minerals are thus never encountered together. Actually, in certain very rare cases, they can be found together. One calls these rocks "triple points" because the conditions under which they were formed correspond to the very precise and unlikely to occur conditions of temperature and pressure where all three can be stable (as in Hamadan in Iran or Sivrihisar in Turkey). The crystals of kyanite are prismatic, often lengthened but also as massive aggregates. They are blue, blue-green to green in color, sometimes gray or black, transparent to opaque, with a pearly lustre.
The most beautiful crystals come from Bahia Brumado in Mians-Gerais and in Barra do Salinas (terminated crystals of 15 cm) in Brazil, in Saint-Gothard/Pizzo-Forno in Switzerland; in Kenya, in India, in Russia. Superb kyanite is also known in Greenland, Norway, Turkey and in the USA.
In France, kyanite is well known in the Armorican massif (Monts d’Arrée, vallée de l’Evel, Baud, Bouvron, Fay), in the Massif Central (Mont Pilat, St Etienne, St Chamond), in the Maures massif (Collobrières)... among many other localities.
the type is kept at the Berwerk Akademie ("School of Mines") in Freiberg, Germany.
Did you know? Kyanite can be used for the manufacture of ceramics because of its great thermal and chemical resistance (esp. to the acids). When of gemmeous quality, and although extremely difficult to cut, it is used in jewellery. But its hardness is different according to the orientation from the crystal (varying from 4.5 to 6.5), which complexifies its cut. Kyanite shares this rare property with… diamond.
HISTORY : Name derived from Greek "κυανοσ" [kyanos] meaning "blue", in reference to its most usual colour
Species described in 1789 by Abraham Gottlob Werner (1749-1817), German geologist from the Freiberg Mining Academy
Type-locality: unknown
ANCIENT NAME : Disthène, cyanite
CHEMICAL FORMULA : Al2 SiO5
CRYSTAL SYSTEM : Triclinic
COLOR : Blue, white, green, yellow or rose
DIAPHANIETY : Transparent to translucent
LUSTER : Vitreous to pearly
STREAK : Colorless
MORPHOLOGIE : Prismatic crystals, flattened
HARDNESS : 5,5-7,0
CHEMICAL CLASS: 3,67
DENSITY : VIII - Silicates
GROUP : Sillimanite-andalousite-kyanite
STRUNZ CLASS BEFORE 2001 : 8/B.02-40
STRUNZ CLASS AFTER 2001 : 9.AF.05
