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Kyanite

kyanite
Rough kyanite

Gem-quality kyanite crystals are pale to deep blue, or white, grey, or green. Colour distribution in crystals may be uneven, with darker blue patches towards the interior.

Kyanite is found in metamorphic gneiss and schist, and in pegmatite veins through metamorphic rocks. It may be weathered out into alluvial deposits. Gem-quality crystals are found in Burma, Brazil, Kenya, and the European Alps. Alluvial deposits are found in India, Australia, and Kenya, and in several localities in United States.

Kyanite crystals have two hardness values: they are softer parallel towards the direction of cleavage, and harder perpendicular into it.

Kyanite Pictures

Rough kyanite

Cause of Color :
  • Blue: Iron and Titanium
  • Green: Vanadium

Chemical Composition :

Aluminium Silicate – Al2SiO5


Classification / Type :

Polymorphous with Andalusite and Sillimanite (Fibrolite)


Crystal System / Forms :

Triclinic System / Bladed crystals and aggregates; polysynthetic twinning.


Cuts & Uses :

Facetted cuts, cabochon, beads, etc.


Dispersion : 0.020
Hardness : 4 and 7, variable hardness in 2 direction (along the length 4 and along the breadth 7)
Lustre : Vitreous
Magnification :

Parallel tube like fissures, cleavage cracks, crystals, color zoning with blue at the center and colorless towards the sides.


Optic Character :

Anisotropic, D.R.; Biaxial negative


Pleochroism : Strong: Violet blue / colorless / blue
Refractive Index / Birefringence :

1.716 -1.731 / ± 0.015; Range: 1.650 – 1.735


Simulants (with separation tests) :

Sapphire (optic figure, R.I., S.G., inclusions), Spinel (optic character), Green Chrysoberyl (R.I., birefringence, inclusions), Tourmaline (optic figure, S.G., inclusions), Idocrase (spectrum, birefringence), Tanzanite (pleochroism, R.I., S.G., inclusions), etc.


Sources :

India, Brazil, Kenya, Myanmar, U.S.A.


Spectrum :

Two strong lines in the deep blue region at 435nm


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