Peridot: A gem mined in antiquity on the Egyptian island of St. John, in the Red Sea. It is a golden-green variety of a mineral called olivine, and includes hues from leek-green to yellow-green. Because of its distinctive green colour, this gem has alternately been confused with emerald and chrysoberyl. Though customarily faceted, peridot has also been polished in a process called Tumbling, or sometimes set in its natural, raw form.