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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
Treatment (Enhancement): 
-
Specific Tests & Remarks: 
-
Synthesis: 
-
Simulants (with key 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.
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