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Formula:   (MgFe)2(SiO4)   mineral photo

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Crystal:   Orthorhombic  
Hardness:   6.5-7  
Spec. Gr.:   3.2-4.3  
Streak:   White  
Cleavage:   Two Imperfect  
Location:   Sapat Kohistan, Pakistan  

Peridot is the gem variety of forsterite which itself is a member of the Olivine group or family. The oldest known deposit of peridot was worked well before Christ on Zabargad Island in Egypt's Red Sea. In his Naturalis Historia, Pliny tells of the first specimen presented to Berenice, Theban queen of Lower Egypt, about 300 BC. The largest known gem peridot crystal was mined on Zabargad and measures 4.5 cm by 3.5 cm, and the largest flawless faceted gem weighs 146 carats, both of which are in the Institute of Earth Science, London. More recently fine peridot crystals have come from the Jalcot Valley of Pakistan (1996). Peridot is colored a warm soft olive or yellowish-green. Tons of tiny pieces of peridot are mined from ant hills in Arizona and New Mexico.

Bibliography: Arem, Joel, Gems and Jewelry, 1975, pg. 101-102.

Bancroft, Peter, Gem and Crystal Treasures, 1984, pg. 289-293.

University of California, Santa Barbara—Department of Earth Science
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