Olivine
Olivine is a magnesium iron silicate, (Mg,Fe)2SiO4, forming a solid-solution series between the magnesium-rich end member forsterite and the iron-rich end member fayalite. It crystallizes in the orthorhombic system and is one of the most abundant minerals in Earth's upper mantle. Its gem-quality green variety, peridot, is one of the few gemstones formed deep within the mantle rather than the crust.
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Olivine properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | (Mg,Fe)2SiO4 |
| Mohs hardness | 6.5–7 |
| Crystal system | Orthorhombic |
| Luster | Vitreous |
| Streak | White |
| Cleavage | Poor, two directions |
| Fracture | Conchoidal |
| Specific gravity | 3.3–4.3 |
| Transparency | Transparent to translucent |
| Common colors | Olive green, Yellowish green, Brown |
| Rarity | common |
Geology & background
Olivine crystallizes early from mafic and ultramafic magmas, making it a major constituent of basalt, gabbro, and peridotite, and it is thought to make up a large share of Earth's upper mantle by volume, giving mantle rock its characteristic green tint where exposed. It also occurs in stony-iron meteorites called pallasites, where striking gem-quality olivine crystals are found embedded in a nickel-iron metal matrix, evidence of the mineral's presence in the cores of shattered ancient asteroids. On Earth, notable gem-quality olivine, or peridot, comes from San Carlos, Arizona, and Zabargad Island in the Red Sea, historically one of the oldest known gem sources in the world.
Rockhounds should be aware that olivine weathers quickly at the surface, altering to a reddish-brown mineral mixture called iddingsite, so fresh, unweathered crystals are most reliably found in recently exposed volcanic rock.
How to identify Olivine
Olivine typically appears as small, rounded, glassy grains or granular masses in dark volcanic rock, ranging in color from olive green to yellow-green, with a vitreous luster and a white to colorless streak. Its hardness of 6.5 to 7 and conchoidal fracture, combined with a lack of visible cleavage, distinguish it from softer green minerals like epidote or chlorite that can occur in similar settings. Olivine is commonly confused with peridot only in gem form, but in rock specimens it is more often mistaken for green pyroxene, which shows distinct cleavage planes that olivine lacks.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Olivine is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Olivine worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Gem-quality olivine, called peridot, has been recovered from stony-iron meteorites called pallasites, making it one of the few gems with an extraterrestrial source.
- Olivine is thought to be one of the most abundant minerals by volume in Earth's upper mantle.
- NASA's Stardust mission and later telescope observations have detected olivine dust around comets and distant young stars.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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