Found in lava, meteorites, and deep in the earth’s mantle, yellow-green peridot is the extreme gem
Gem miners find peridot as irregular nodules (rounded rocks with peridot crystals inside) in some lava flows in the United States, China, and Vietnam and, very rarely, as large crystals lining veins or pockets in certain types of solidified molten rock. Sources for the latter include Finland, Pakistan, Myanmar, and the island of Zabargad.
Geologists believe both types of deposits relate to the spreading of the sea floor that occurs when the earth’s crust splits, and rocks from its mantle are pushed up to the surface. Sometimes—as in Myanmar— these rocks can be altered, deformed, and incorporated into mountain ranges by later earth movements.
Rarely, peridot can have an extraterrestrial source, being contained in meteorites that have fallen to earth.
The color range for peridot is narrow, from a brown-green color to yellowish green to pure green. Yellowish green is the most common peridot color seen in jewelry.
Peridot is the gem variety of the mineral olivine. Its chemical composition includes iron and magnesium, and iron is the cause of its attractive yellowish green colors. The gem often occurs in volcanic rocks called basalts, which are rich in these two elements.
BIRTHSTONES & ANNIVERSARIES
Peridot is the birthstone for August and the 15th anniversary gemstone.
COLOR: Yellowish green
REFRACTIVE INDEX: 1.65 to 1.69
BIREFRINGENCE: 0.035 to 0.038
SPECIFIC GRAVITY: 3.34
MOHS HARDNESS: 6.5 to 7
WHY WE LOVE THIS GEMSTONE
Peridot crystals are found in meteorites: some rare extraterrestrial crystals are even big enough to facet as cut gemstones.
Most gems are colored by impurities such as iron. Peridot's color is intrinsically yellow-green. Higher-quality stones have an intense color.
Peridot has extremely high double refraction: when you look closely through the gem, you can see two of each pavilion facet.