The August birthstone, peridot has been prized as a jewelry stone since ancient times. Always green in color, but with considerable variations, a peridot's particular shade depends on its source. Peridots have been credited with protecting their wearer during the night. This is due to the fact that the lively appearance of peridot fostered ancient associations between the gemstone and the sun. It was thought that keeping the stone close during dark hours repelled nighttime evil spirits.
(International Gem Society)