August - the birthstone for August is the peridot.
Peridot (pronunciations of per' i doe and per' i dot are both considered correct) belongs to the forsterite-fayalite mineral series, which is part of the olivine
group. It is one of the "idiochromatic" gems, meaning its color comes from the basic chemical composition of the mineral itself, not from minor impurities, and therefore will only be found in shades of green. As a matter of fact peridot is one of the fewgemstones found in only one color.
The name peridot most probably derives from the Arabic word "faridat" for gem. It's also called chrysolith (derived from the Greek word "goldstone") and olivine, because of its color and membership to the olivine group.
Gem quality peridot comes from Arizona, Burma, Norway, islands in the Red Sea, Hawaii and is sometimes found in meteorites. It's been mined as a gemstone for thousands of years, and is mentioned in the Bible under the name of Chrysolite. Legend says that peridot was one of the favorite gemstones of Cleopatra and that some of the "emeralds" worn by her were actually peridot.
Historically the volcanic island Zabargad (St. John) in the Red Sea, east of Egypt, was the most important deposit that was exploited for 3500 years. Today's main deposits are in Arizona, China, Vietnam and Pakistan. The Pakistani peridot in particular is very fine, and a new find in Pakistan in the mid-1990's has made peridot available to a wider market.