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

Kyanite Properties

Chemical Composition: 
Aluminium Silicate - Al2SiO5
Classification / Type: 
Polymorphous with Andalusite and Sillimanite (Fibrolite)
Colors / Varieties: 
  • Blue, green, colorless, pink, yellow, black Transparency: Transparent to Opaque.
  • Chatoyant varieties.
Crystal System / Forms: 
Triclinic System / Bladed crystals and aggregates; polysynthetic twinning.
Hardness: 
4 and 7, variable hardness in 2 direction (along the length 4 and along the breadth 7)
Specific Gravity: 
3.65 - 3.70
Cleavage / Fracture: 
Easy 1 directional pinacoidal cleavage, 1 directional parting (collectively appears as 2 directional cleavage) / Uneven fracture
Optic Character: 
Anisotropic, D.R.; Biaxial negative
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.716 -1.731 / ± 0.015; Range: 1.650 - 1.735
Pleochroism: 
Strong: Violet blue / colorless / blue
Dispersion: 
0.020
Magnification: 
Parallel tube like fissures, cleavage cracks, crystals, color zoning with blue at the center and colorless towards the sides.
U.V. Fluorescence: 
Variable, commonly weak red under longwave
Spectrum: 
Two strong lines in the deep blue region at 435nm
Cause of Color: 
  • Blue: Iron and Titanium
  • Green: Vanadium
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.
Geological Occurrence: 
In schists and gneisses associated with staurolite, garnet, rutile, lazulite and corundum.
Sources: 
India, Brazil, Kenya, Myanmar, U.S.A.
Cuts & Uses: 
Facetted cuts, cabochon, beads, etc.