Peridot

Peridot is the gem-quality variety of the mineral olivine, a magnesium-iron silicate. It is one of the few gemstones that occurs in essentially one color — a distinctive yellowish, olive, to lime green — caused by iron that is an essential part of its structure rather than a trace impurity (an 'idiochromatic' gem).

It crystallizes in the orthorhombic system and is known for strong double refraction, giving cut stones a slightly doubled, sparkling appearance. Hardness is moderate (6.5-7).

Peridot has been mined for thousands of years (ancient Egyptians called it the 'gem of the sun'), and it is the birthstone for August. It is even found in some meteorites.

Peridot forms deep in the Earth's mantle and is brought to the surface in basaltic lavas and in mantle xenoliths — chunks of mantle rock carried up by erupting volcanoes. Olivine is one of the most abundant minerals in the upper mantle.

Gem-quality crystals are found weathered out of these volcanic rocks, as on Arizona's San Carlos Reservation and Hawaii's green-sand beaches. A different, important source is the historic island of Zabargad (St. John's Island) in the Red Sea, and high-quality crystals come from Pakistan and Myanmar.

Remarkably, peridot also occurs in stony-iron (pallasite) meteorites, making it a truly extraterrestrial-capable gem.

Peridot is recognized by its lively yellow-green to olive color, vitreous-to-oily luster, hardness of 6.5-7, and strong double refraction — looking through a cut stone, the back facets appear doubled. Streak is white/colorless.

It commonly contains 'lily pad' disk-like inclusions. Its color is consistent and does not vary much by lighting.

Look-alikes: Green tourmaline, emerald, green garnet (tsavorite/demantoid), and chrysoberyl can resemble it, but peridot's distinctive oily green and obvious facet doubling are key. Glass imitations lack double refraction and inclusions. Demantoid garnet is harder and singly refractive.

Peridot is used almost entirely as a gemstone, faceted for rings, pendants, and earrings, and prized for its bright, cheerful green. Larger, more saturated stones from Pakistan and historic Zabargad material are the most valuable.

Its moderate hardness makes it suitable for jewelry with reasonable care, avoiding hard knocks and harsh chemicals. Fine crystals and pallasite-meteorite peridot are also collected.

As the August birthstone, peridot has a long history as a protective talisman associated with light, warmth, and warding off negativity. Metaphysically it is linked to renewal, abundance, and emotional healing.