Peridot, spinel and sardonyx are the three birthstones for August. The peridot birthstone is known for being formed under extreme conditions, as it can be found in the hardened lava that carried it from deep within Earth’s mantle as well as in meteorites that traveled from outer space. The spinel birthstone was underappreciated until recently, as today’s consumers look for an alternative to ruby, a gem with which red spinel was mistaken for centuries. Sardonyx is the original August birthstone, with a history that dates back more than 4,000 years.