Peridot is gem-quality olivine, which is a silicate mineral. Peridot is one of the few gemstones that occur in only one color, olive green. The intensity and tint of the green, however, depends on the percentage of iron that is contained in the crystal structure, so the color of individual peridot gems can vary from yellow, to olive, to brownish-green. Peridot is rated between 6.5 and 7 on the Mohs hardness scale.  Peridot is thought to promote independence; dissipate anger and promote one to admit mistakes.