Kornerupine

Although kornerupine was named in 1884, it was not until 1912 that gem-quality material was found. Even now it is uncommon and cut only for collectors. Strongly pleochroic, it appears green or reddish brown when viewed from different directions. To show the very best colour, it is cut with the table facet parallel to the length of the crystal.

Localities include Madagascar, Sri Lanka, and East Africa, which also produces an emerald green variety. Cat’s eye gems are cut from Sri Lankan and East African stones.

It has been confused with tourmaline and enstatite.

Kornerupine Properties

Chemical Composition: 
Borosilicate of magnesium, iron and aluminium - Mg3Al6(Si,Al,B)5O21(OH)
Colors / Varieties: 
Green, greenish yellow, greenish brown, brownish yellow. Chatoyant and Star (rare) variety.
Crystal System / Forms: 
Orthorhombic System / Prismatic crystals, fibrous and columnar.
Hardness: 
6.5
Specific Gravity: 
3.28 - 3.35
Cleavage / Fracture: 
Perfect 2 directional / Conchoidal fracture.
Optic Character: 
Anisotropic, D.R.; Biaxial negative (pseudo-uniaxial)
Lustre: 
Vitreous
Refractive Index / Birefringence: 
1.665 - 1.678 / 0.013 - 0.017; Range: 1.664 - 1.683
Pleochroism: 
Strong: green / yellow, reddish brown
Dispersion: 
0.018
Magnification: 
Crystalline inclusions (zircon, apatite), fine needles.
U.V. Fluorescence: 
Varies from inert to yellow in longwave and shortwave.
Spectrum: 
Line at 503nm
Cause of Color: 
Traces of iron, chromium, vanadium.
Simulants (with separation tests): 
Tourmaline (optic figure, R.I., birefringence, spectrum), Enstatite (spectrum, pleochroism), Diopside (R.I., birefringence, spectrum), Sinhalite (R.I., birefringence, spectrum), Spodumene (R.I., S.R., U.V. fluorescence), etc.
Geological Occurrence: 
In alluvial deposits.
Sources: 
Sri Lanka, Myanmar, Kenya, Tanzania, Madagascar, Canada, Nepal.
Cuts & Uses: 
Facetted cuts and cabochons.