Peridot

Peridot: A Messenger from the Earth's Mantle and Outer Space Peridot is the gemstone variety of olivine, a solid solution between forsterite (Mg₂SiO₄) and fayalite (Fe₂SiO₄). It is an idiochromatic gemstone, meaning its signature green color is derived directly from its structural chemical composition—specifically the presence of iron (Fe²⁺) —rather than external impurities.

Deep Geology and Extraterrestrial Origins Peridot is one of the few gemstones that does not form in the Earth's crust, but rather under the extreme pressure and temperature conditions of the upper mantle, often at depths exceeding 100 km.

• Magmatic Ascent: It reaches the surface via volcanic eruptions, transported by magmatic rocks such as basalts. Famous deposits include Zabargad Island (Egypt), Myanmar, and the United States (Arizona).

• Cosmic Origin: Uniquely in gemmology, peridot is also found in pallasites, meteorites composed of olivine crystals embedded within an iron-nickel matrix. These specimens are genuine fragments of asteroids.

Physical Properties and Diagnostic Inclusions With a Mohs hardness of 6.5 to 7, peridot is a vibrant gemstone but remains sensitive to mechanical stress and thermal shock.

• "Lily Pad" Inclusions: During laboratory expertise, we often look for chromite inclusions surrounded by circular stress fractures. These patterns, known as "lily pads," are characteristic of peridot and reflect the decompression the crystal underwent during its journey to the surface.

• Optics: It features strong double refraction (birefringence). Through a loupe, one can often observe a doubling of the pavilion facet edges, an optical signature that easily distinguishes it from imitations.

Care and Precautions Peridot is sensitive to acids and sudden temperature changes. Ultrasonic and steam cleaning are strongly discouraged. Cleaning with lukewarm soapy water and a soft cloth is the safest method to preserve its vitreous luster.