Gem quality specimens of the mineral olivine are called peridot by gemmologists. Peridot has an olive or bottle green colour due to the presence of iron, and a distinctive oily or greasy lustre. It has a high birefringence, so doubling of the back facets can easily be seen in larger specimens when viewed from the front. Good-quality crystals are very rare.
Peridot is found on St. John’s Island (Egypt), in China, Burma, Brazil, Hawaii and Arizona (USA), Australia, South Africa and Norway.
The Crusaders brought peridot to Europe in the Middle Ages, transporting stones from St. John’s Island in the Read Sea, where it had been mined for over 3,500 years.