It's time for retail jewelers to begin promoting the birthstone for August—peridot. While in the past it's taken concentrated effort to sell this lime-green gem, today's fashion flashback to the '70s might make this the perfect time for peridot. But that doesn't mean it will sell itself. Even when it's the featured gem, as in a magnificent antique necklace worn at this year's Academy Awards by actress/model Nastassja Kinski, public recognition is what counts. Kinski's necklace was noticed twice by People magazine but then disappointingly described—first brushed off as an accent stone, labeled as gold and diamonds with "semiprecious light-green peridots," then mentioned again as an unnamed gem in a "gorgeous emerald-colored necklace." History and name. Peridot's history begins on a small desert island 50 miles or so off the southeast coast of Egypt in the Red Sea. The name of the