310-carat fine-quality Peridot from Zebirget, Egypt, is the largest known. Peridot is the gem name for a yellow-green mineral that occurs in volcanic rock. The mineral's species name is Torsterite. Most of the world's supply in mined in Arizona, hand-hammered out of basalt. A transparent gem, Peridot has a distinctive oily luster. The color ranges from pale golden-green to brownish green. From the Gem and Mineral collection of the Smithsonian's National Museum of Natural History.