igneous
Olivine-rich peridotite / olivine crystal fragment
Olivine, typically (Mg,Fe)₂SiO₄; possibly peridotite if the specimen is rock rather than a single crystal
AI-generated identification · may be incorrectOlive-green to yellow-green, glassy to resinous luster, granular texture, and no obvious cleavage; olivine hardness is 6.5–7 Mohs and specific gravity about 3.2–4.4. The image alone cannot confirm whether it is gem-quality forsterite or matrix-rich peridotite.
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Physical properties
Olive-green to yellow-green, glassy to resinous luster, granular texture, and no obvious cleavage; olivine hardness is 6.5–7 Mohs and specific gravity about 3.2–4.4. The image alone cannot confirm whether it is gem-quality forsterite or matrix-rich peridotite.
Formation & geological history
Olivine crystallizes from magnesium- and iron-rich magma and is a major mineral of Earth’s upper mantle; exposed specimens commonly come from basaltic rocks, ultramafic peridotites, or volcanic nodules. Earth formation is ancient, though the particular fragment’s age is unknown.
Uses & applications
Gem-quality transparent olivine is called peridot and is used in jewelry; ordinary olivine/peridotite is mainly a collector material and has limited refractory or aggregate applications.
Geological facts
Fresh olivine is commonly olive green but alters readily to brown iddingsite or serpentine. It lacks the strong cleavage typical of many silicate minerals and commonly shows conchoidal or uneven fracture.
Field identification & locations
Look for a dense olive-green grain, glassy luster, poor cleavage, and hardness sufficient to scratch window glass; distinguish it from green glass by its natural uneven texture and heft. Common sources include Arizona, Hawaii, Pakistan, Myanmar, Egypt, and mantle-derived rocks worldwide.
