The ancient Egyptians mined peridot on the Red Sea island of Zabargad, the source for many large fine peridots in the world’s museums. The Egyptians called it the “gem of the sun.” Today this gem is still prized for its restful yellowish green hues and long history. Large strongly-colored, examples can be spectacular, and attractive smaller gems are available for jewelry at all price points.
In 2005, peridot was found in comet dust brought back from the Stardust robotic space probe
Some peridot is ancient: it's found in pallasite meteorites, remnants of our solar system's birth.
Most gems are colored by impurities such as iron. Peridot's color is intrinsically yellow-green. Higher-quality stones have an intense color.
Peridot has extremely high double refraction: when you look closely through the gem, you can see two of each pavilion face
Most fine peridot is eye clean. Tiny black spots might be visible with magnification.
Although the best peridot is a pure grass green, most peridot is yellowish-green
Peridot is cut in a wide variety of styles, including ovals, emerald cuts, and cushions
Large crystals of peridot have cut gems more than 50 carats in size.
More info: http://www.gia.edu/peridot