Sinhalite

Until 1952, sinhalite was thought to be a brown variety of peridot, but on closer investigation it was found to be a completely new mineral. It varies from a pale yellowish brown to a dark greenish brown. Crystals have distinct pleochroism, showing pale brown, greenish brown, and dark brown when viewed from different directions. Although uncommon, sinhalite has been faceted for the collector. Cut stones may be confused with peridot, chrysoberyl and zircon.

Most gem quality sinhalite is found as rolled pebbles in the gem gravels of Sri Lanka. Crystals occur in Burma but are rare. Sinhalite is also found within the former USSR and non-gem quality material in the United States.

Sinhalite is named after “sinhala”, which is the Sanskrit name for Sri Lanka.

Cause of Color :

Iron

Chemical Composition :

Magnesium Aluminum Borate – MgAlBO4

Crystal System / Forms :

Orthorhombic System / Grains and rolled pebbles.

Cuts & Uses :

Facetted cuts, cabochon, etc.

Dispersion : 0.018
Hardness : 6.5
Lustre : Vitreous
Magnification :

Crystalline inclusions, doubling

Optic Character :

Anisotropic, D.R.; Biaxial negative

Pleochroism : light brown, dark brown and greenish brown
Refractive Index / Birefringence :

1.670 – 1.708 / 0.038. Range: 1.667 – 1.711

Simulants (with separation tests) :

Peridot (pleochroism, spectrum), Tourmaline (optic figure, R.I. birefringence, S.G., spectrum), Chrysoberyl (R.I., birefringence, S.G., spectrum), Kornerupine (birefringence, spectrum), Epidote (R.I., birefringence, spectrum)

Sources :

Sri Lanka, Myanmar

Specific Tests :

Doubling is seen.

Spectrum :

Bands at 452nm, 463nm, 475nm, 493nm.

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