Cause of Color :
Iron – due to ferrous iron (ideally 12% – 15%). Presence of chromium gives a brighter green.
Chemical Composition :
Silicate of magnesium and iron where iron is generally 12% – 15%, Cr, Mn & Ni may also be present. (MgFe)2SiO4
Classification / Type :
Mineralogically known as Olivine, peridot belongs to the isomorphous Forsterite (Mg) – Fayalite (Fe) series.
Crystal System / Forms :
Orthorhombic System / Striated prisms, rolled pebbles, crystals are rare.
Cuts & Uses :
Facetted cut, cabochon, beads, carvings, etc.
6.5 - 7 (Fayalite - Forsterite)
Oily to vitreous.
Lily pad inclusions are halos with a crystal (chromite or chrome spinel) at the centre, glass balls that look like bubbles (Hawaiian), rectangular biotite crystals, doubling.
Optic Character :
Anisotropic, D.R.; Biaxial positive.
Refractive Index / Birefringence :
1.654 – 1.690 / 0.036. Range: 1.640 – 1.700
Simulants (with separation tests) :
Sinhalite (pleochroism, spectrum), Diopside (R.I., spectrum), Tourmaline (optic figure, R.I., S.G., pleochroism), Apatite (R.I., birefringence, inclusions, spectrum), Fluorite (optic character), Glass (optic character), Synthetic Spinel Triplet (optic character, inclusions)
Hawaii, Zeberged (Egypt), Isle of St. John, Myanmar, Pakistan, Norway, Kenya, U.S.A. (California, New Mexico and Arizona).
Specific Tests :
- Doubling is seen.
- Brittle stone.
- Attacked by acids.
Bands at 493nm, 473nm & 453nm.