A pale-green or yellow-green
gemstone of the
olivine family. (
Gorgonzola tells me it's "specifically
gem-quality
Forsterite (Mg2SiO4).")
Chrysolite, given as the same thing is
Webster 1913's writeup, is really a generic term for gems of the same color, including
chrysoberyl. Some peridots have wound up labeled as
emeralds if they had a deep enough color, and historically peridot was considered to be the same thing as
topaz and the
Red Sea island where it was first mined was even called Topazios (it's now
Zabargad), but modern
mineralogy sorted out their different compositions.
Currently almost 80% of peridot on the market comes from Arizona, but many other locations produce small amounts. Peridot itself is not rare, but large crystals of the stone are.