Olivine

Overview

Olivine is a family of magnesium–iron silicate minerals whose general formula is (Mg,Fe)2SiO4. It belongs to the broader class of silicate minerals and forms a continuous solid solution between the magnesium-rich endmember forsterite and the iron-rich endmember fayalite. The common name chrysolite is sometimes used in older literature. In gem-quality, transparent crystals the mineral is known as peridot.

Characteristics and structure

Olivine typically appears in shades of green ranging from yellow-green to deep olive. Its physical properties vary with iron content: increasing magnesium favors lighter, more yellow-green tones, while higher iron shifts color and increases density. The mineral crystallizes in the orthorhombic system and usually forms granular to compact aggregates rather than well-developed large crystals in most rocks.

Occurrence and geologic context

Olivine is a major constituent of ultramafic igneous rocks such as peridotite and dunite (rocks that can be composed of more than 90% olivine). These rocks are abundant in the upper part of the Earth's mantle and are commonly brought to the surface as xenoliths in basaltic lavas or as fragments in ophiolite complexes. Where mantle slices are emplaced on continents during tectonic thrusting, olivine-rich rocks may be exposed on land rather than buried beneath the crust via subduction-related processes and tectonic emplacement. Olivine also occurs in mafic igneous rocks such as basalt and gabbro and is observed in meteorites and lunar samples, which links it to early planetary formation and magmatic activity.

Alteration, stability and significance

At Earth's surface conditions olivine is relatively unstable and weathers chemically to form secondary minerals such as serpentine, iddingsite and clays through hydration and oxidation. Its high-temperature stability in the mantle makes it a useful indicator mineral for interpreting mantle melting, mantle composition and thermal history. In planetary science, the presence of olivine in meteorites, on the Moon, and in dust around young stars is taken as evidence of high-temperature igneous or condensational processes in the early solar system.

Uses and notable facts

Gem-quality olivine (peridot) has been valued as a gemstone since antiquity. Industrially, olivine sand is used as a refractory material and as a foundry sand because of its high melting point and chemical properties. More recently, researchers have explored olivine's role in environmental applications such as enhanced weathering and mineral carbonation for carbon dioxide capture because its magnesium and calcium content can react with CO2 to form stable carbonate minerals.

• Composition and formula: (Mg,Fe)2SiO4; solid solution between forsterite and fayalite.
• Common rocks: dunite and peridotite (mantle-derived), basalt and gabbro (volcanic and plutonic).
• Gemstone name: peridot; often mistaken for other green gems.
• Extraterrestrial occurrences documented in lunar samples, meteorites and protoplanetary dust—useful for planetary studies (mantle and planetary interiors).
• Links to chemistry and material science: silicate structure, magnesium content, and iron variation.
• Geologic processes: uplift and emplacement from depth (subduction, obduction).

Olivine remains a mineral of wide interest across geology, gemology and emerging environmental technologies because its chemistry records mantle processes and because its reactions at Earth’s surface offer practical possibilities for mineral-based carbon sequestration. For general mineralogical descriptions see more detailed references on silicates and petrology sources (mantle studies).