Peridot is one of the few stones that naturally occurs in only one color, olive green. The varying amount of iron contained in the type of crystal that forms this gemstone is what determines the shade of olive green. Peridot’s colors range from yellowish-green, dark olive green, to brownish green. Although peridot is abundantly found, formed in lava from volcanoes and even meteorites, gem quality material is quite rare. The most valuable and desired peridot is dark olive green. Peridot is the birthstone for August.