Peridot is the gem variety of the mineral Olivine. It is a iron magnesium silicate. The hue of the green depends on how much iron content is in the crystal structure. The colors range from a bright limey yellowish green to a deep luscious leaf green of the stones from the High Himalayas of Pakinstan. It is a very undervalued gemstone at the moment.
Peridot is the official birthstone of August. It is said to possess magical powers and healing properties. It can be found in Egyptian jewellery from the early 2nd millennium B.C, when the stones came from Aswan. The Romans canned it ‘the emerald of the evening’.
It is only ever green. Peridot from Arizona tends to be lime green with a brown tinge, from China it is lime green, from Pakistan it is line green to deep leaf green and from Burma it is Apple Green. Cats eye stones and star stones are rare. Peridot has strong birefringence: also known as double refraction (where the decomposition of a ray of light is split into two rays) More evident in larger stones, so through the table the back facets may be doubled.
Hardness on Mohs Scale: 6.5 Toughness: Fair to Good
Luster: Vitreous Specific Gravity: 3.32-3.37
Refractive Index: 1.65-1.69Birefringence*: 0.036 - biaxial
Chemical Formula: (Mg, Fe)2 SiO4
Crystal Habit: Prismatic well formed crystals come from Pakistan. Elsewhere it tends to be crystal fragments or rolled pebbles. Crystals have orthorhombic prisms with a rhombus shaped cross section, broken or rounded surfaces, with a dull, vitreous/greasy luster.
In Pakistani stones look for ludwigite hair, ‘silk’ and rod like inclusions. Also black chromite crystal inclusions surrounded by small stress fractures that resemble water-lillies, finger print inclusions. Brown Mica flakes are more evident in Arizona gems.
Saydan, Dar, Manrka-Kheil and Kurri mines in Pakistan. The Saydan and Dar mines have recently closed due to glacier slides. Burmese Peridot: Pyaung Gaung, Hebei province - China & Peridot Mesa, San Carlos in Arizona.
Small stones are very reasonable but when the stones pass four carat they become more expensive. The 4C’s apply as always. Depth and richness of color greatly affects value.
Occasionally we have found epoxy resin filling, but it is not common place.
Peridot is such an underrated gemstone. Like many gemstones, it is not played with by the ‘hot houses’ in Thailand to change the color. We have found Peridot with a more sumptuous green color than the best green Tourmaline. To me there is nothing better. A great value gemstone that is oh so beautiful.
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