igneous
Peridotite Xenolith (Olivine)
Peridotite (predominantly Forsterite, (Mg,Fe)2SiO4)
Olive green to dark greenish-brown color, grainy to crystalline texture, earthy to vitreous luster, Mohs hardness 6.5-7 (for olivine grains), dense and heavy due to high iron and magnesium content, porous or vesicular host rock matrix.
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Physical properties
Olive green to dark greenish-brown color, grainy to crystalline texture, earthy to vitreous luster, Mohs hardness 6.5-7 (for olivine grains), dense and heavy due to high iron and magnesium content, porous or vesicular host rock matrix.
Formation & geological history
Forms deep within Earth's upper mantle under extreme temperature and pressure. Transported to the surface rapidly by violent explosive volcanic eruptions (basaltic lavas or kimberlites) as xenoliths (foreign rock fragments).
Uses & applications
Used primarily for geological research to study Earth's mantle composition. Olivine rich varieties (gem-quality) are cut into peridot gemstones. Industrial olivine is used as a flux in steel making and refractory sand.
Geological facts
Peridotite nodules provide scientists with actual physical samples from the Earth's mantle, tens to hundreds of kilometers below the crust. Gem-quality olivine from these nodules is known as peridot, the birthstone for August.
Field identification & locations
Identified by its distinctive yellowish-green to olive-green sugary crystals embedded within dark volcanic host rock. Commonly found in basaltic lava fields, volcanic pipes, and oceanic crust deposits worldwide.
