Peridot is gem-quality olivine. As peridot is the magnesium-rich variety (forsterite) the formula approaches Mg2SiO4. Peridot is one of the few gemstones that occur in only one color, an olive green. The intensity and tint of the green, however, depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow--to olive--to brownish-green. The most valued color is a dark olive-green.

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