Peridot
PERIDOT, the gem variety of OLIVINE, is the official August birthstone. Although it occurs in several locations worldwide, it is most famously found on the San Carlos Indian Reservation in southern Arizona, where 80-95% of the world supply of peridot is produced.
Olivine is composed of two minerals, and ranges from magnesium-rich (fayalite) to iron-rich (forsterite). It has strong birefringence, which means when you look into the gem you will often see a doubling of the facet edges and you can see a doubling of the inclusions as well.
Variety of: olivine ♦ Chemistry: iron magnesium silicate ♦ Color: yellow, olive green, brownish, lime green, emerald green ♦ Crystal system: orthorhombic ♦ Cleavage: poor ♦ Fracture: conchoidal ♦ Moh's hardness: 6.5-7 ♦ Luster: vitreous ♦ Transparency: transparent to translucent ♦ Localities: Arizona, California, New Mexico, Myanmar (Burma), islands of the Red Sea, Kohistan, Pakistan, Germany, Mexico, Norway, Hawaii.