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A very large peridot about the size of a very large potatoe ( probably weighing over three hundred carats) was bought by a French gem dealer more than thirty years ago. Some years later the stone appeared on the cover of a famous magazine with Brook Shields as the model. This stone remains the finest and biggest cut peridot to this day. Until recent years, the finest peridot came from Burma. Then there was the discovery of smaller sizes and more yellowish colored peridot "gravels" from the Indian reservations in Arizona. They were however more included with the typical "lily pad" like inclusions. Some were cuttable and most were tumbled and drilled to make necklaces.
Then came China and its productions. The Chinese materials were maninly smaller in size under 3 carats and lighter in shades. Still none came close to the Burmese peridot in color instensity or brilliance. Then came the mines in Pakistan which were producing some of the finest ever found. The colors were deep and clear. The crystal purity contain almost zilch brown. They were on par if not superior to Burma peridot. Alas, the mines in Pakistan/Afghanistan border were interupted with the war on Osama Bin Laden and production was sporadic and quantities dwindled. Mostly German dealers got ahead start and managed to get a few good deals until travelling became hazardous and if not impossible in the embattled war zone.
Lately, world demand has pushed up prices and remains strong for the time being. Also known as olivine, it is called fosterite when Mg is present and fayalite when iron is present. Peridot however is the term most commonly used in the gem trade to refer to this gem. Fosterite shows green hues to pale lemon yellow. Fayalite displays green, yellowish green, amber brown, brown, olive, green. The color of peridot is due to ferrous iron. The best green is supposed to contain an iron content of about 12 to 15%. More Fe would result in a darker brownish color. Very bright green has shown traces of Cr.
Chemical formula is Mg2SiO4-Fe2SiO4. Mn is rarely present. Crystal habbit is orthorhombic, crystals are rare especially well formed ones, usually striated, elongated and eroded, often as rounded pebbles. Luster is vitreous. Hardness is 6.5 - 7. Cleavage is imperfect to weak. Fracture is conchoidal. Brittle. Birefringence is strong ranging from 0.035 to 0.052. Distinct doubling of facet junctions can be observed. Refractive index is 1.635 to 1.654 and may vary with chemical composition.
Egypt and Norway are known to have produced peridot but not in commercial quantities and not in recent times. Cat's eye and star variety have been reported. Peridot is the birthstone for August and remains a big favorite among gem enthusiats and collectors. Its unique green has been a source of universal appeal for this fine gemstone. |
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