Sinhalite gemstone

by Manisha G

image of sinhalite gemstoneA gemstone discovered in 1952, formerly thought to be “brown peridots”. It may have confused with brown chrysoberyl, tourmaline or brown zircon in appearance.

Chemical composition: Borate of magnesium, iron and aluminium. The iron content can vary considerably and is the cause of the colour.

Crystal characteristics: Orthorhombic system with structure similar to peridot.

Habit: Fairly large pieces have been found as water worn pebbles. Complete crystals so far examined indicate a habit similar to that of peridot. The stone is much rare than peridot.

Varieties: From pale yellow or straw colour to dark brown and black depending on iron content. Colour can vary with the direction of cutting owing to dichroism. Some greenish-brown stones also occur.

Physical properties:

Cleavage: Cleavage cracks occur but their crystallographic direction is not yet known.

Hardness: 6.5

S.G.: 3.47 to 3.49

Lustre: Vitreous

Refraction: Double, Biaxial, negative sign; R.I.: 1.670 to 1.708; D.R.: 0.038

Spectrum: 4520, 4630, 4750, 4930 A° (Bands)

Dichroism: Distinct, colours green and brown, D.R. can be seen with a lens as a doubling of back facets.

Cut: Mixed and trap or step cut.

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