Cluster of green PERIDOT crystals. Peridot is a green, gemmy variety of Forsterite (Olivine). The largest Peridot crystal is 1.1 inches in length. From Pakistan. Peridot is a highly desirable precious gemstone. Peridot is the birthstone for the month of August and the 16th wedding anniversary gemstone. This piece is from the collection of Roger Maynard. Roger is a friend and long-time geologist with the US Geological survey in New Mexico.