Quick Facts
Formation & Origin
Olivine is one of the first minerals to crystallize from cooling basaltic magma, forming at temperatures between 1200 and 1900 degrees Celsius depending on composition. It is the dominant mineral in Earth's upper mantle, making up approximately 50 to 60 percent of peridotite rock from depths of about 30 to 400 kilometers. The mineral forms a solid solution series between the magnesium-rich end member forsterite (Mg₂SiO₄) and the iron-rich end member fayalite (Fe₂SiO₄). Mantle olivine is typically forsterite-rich (Fo₈₈₋₉₂), while olivine in basaltic lavas tends to be more iron-rich.
In volcanic settings, olivine crystallizes early from mafic magmas deep in the crust or upper mantle. These early-formed crystals are often carried to the surface as xenocrysts within erupting basalt, which is why olivine grains are commonly found embedded in basalt flows worldwide. At the San Carlos locality in Arizona, olivine-bearing mantle xenoliths (chunks of upper mantle rock) were ripped from depth by ascending basaltic magma and deposited at the surface. Weathering frees the durable olivine crystals from the softer basalt matrix.
Perhaps olivine's most remarkable occurrence is in pallasite meteorites. These rare meteorites contain gem-quality olivine crystals suspended in an iron-nickel metal matrix. They are believed to originate from the core-mantle boundary of small, differentiated protoplanets that were destroyed by collisions early in the solar system's history. The olivine represents the silicate mantle material, while the metal represents the metallic core. Pallasite olivine has been dated to approximately 4.5 billion years old, making it among the oldest mineral specimens available to collectors.
Identification Guide
Olivine is identified by its characteristic olive to yellow-green color, vitreous to greasy luster, and granular or stubby prismatic crystal habit. In basalt, it appears as small, glassy green grains or rounded phenocrysts. Gem-quality peridot shows a distinctive oily or greasy luster that distinguishes it from other green gems. Hardness is 6.5 to 7, and the mineral has conchoidal fracture rather than prominent cleavage, which helps distinguish it from green pyroxenes that show distinct cleavage at near-90-degree angles. The specific gravity is notably high (3.22-4.39, increasing with iron content), so olivine feels heavy for its size. Distinguish from green tourmaline by olivine's orthorhombic system and lack of strong pleochroism. Distinguish from green glass by olivine's higher specific gravity and characteristic inclusions (lily pad discs, black chromite crystals). In thin section under a petrograph, olivine shows high relief, bright second-order interference colors, and a distinctive cracked appearance.
Spotting Fakes
For gem peridot, the most common imitation is green glass, which can be identified by its lower specific gravity and lack of natural inclusions. Genuine peridot almost always contains tiny black chromite crystal inclusions and characteristic disc-shaped stress fractures called lily pads, visible under 10x magnification. Glass will show bubbles instead. Synthetic peridot does not exist commercially, so any genuine-looking stone is likely either real or glass. Green cubic zirconia and green synthetic sapphire are sometimes sold as peridot, but both have much higher refractive indices and different optical properties visible with a refractometer. Peridot has a distinctive doubling of back facet edges when viewed through the table with a loupe, due to its strong birefringence. Glass will not show this doubling. For rough specimens, test hardness (6.5-7) and check for the characteristic greasy luster. Dyed quartz sold as peridot will show color concentration in fractures under magnification.
Cultural & Metaphysical Traditions
Presented as cultural traditions, not scientific evidence
Olivine in its gem form peridot is one of the oldest known gemstones, used by ancient Egyptians who called it the gem of the sun. The Egyptians mined peridot on Zabargad Island in the Red Sea as early as 1500 BCE, and some scholars believe Cleopatra's famous emerald collection may have actually been peridot. In medieval European tradition, peridot was set in gold and worn as a talisman against nightmares and enchantments. Hawaiian tradition holds that peridot crystals are the tears of Pele, the volcano goddess. In Islamic tradition, peridot was highly valued and frequently used to adorn mosques. The mineral has been associated with warmth, vitality, and protection across many cultures throughout history.
Where It's Found
Ancient source of gem peridot, mined by Egyptians since at least 1500 BCE. Olivine occurs here in altered peridotite host rock.
World's most prolific source of gem peridot. Olivine xenoliths in basalt are weathered free and collected from the desert surface.
Papakolea Beach (Green Sand Beach) is composed almost entirely of olivine crystals eroded from surrounding basalt.
Produces large, exceptionally fine gem peridot crystals from metamorphosed limestone near ultramafic intrusions.
Olivine crystals embedded in iron-nickel matrix in pallasite meteorites represent material from the core-mantle boundary of destroyed protoplanets.
Price Guide
Good to Know
Scratch test: At hardness 7, Olivine can scratch glass and steel. It's durable enough for any type of jewelry.
Sources: Found in 5 notable locations worldwide, from Zabargad Island to Pallasites (meteorites).
Heft test: Olivine has average mineral density (3.22-4.39). It feels about as heavy as you'd expect from a stone its size.
Related Minerals
Gem-quality variety of olivine used in jewelry
Common mantle silicate that coexists with olivine in peridotite
Hydrated alteration product formed when olivine reacts with water