This common mineral makes up the bulk of the Earth's upper mantle

Nature · Published 3 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Olivine is more than just a pretty green gemstone. As the most abundant mineral in the Earth's upper mantle, it dictates the flow of solid rock that drives plate tectonics. Beneath the surface, this silicate mineral holds secrets about our planet's deep water storage and the birth of stars.

Olivine is not a single mineral but a group of magnesium and iron silicates. Its name reflects its characteristic yellow-green to bottle-green hue, though gem-quality forsterite—known as peridot—is the most famous variety. Structurally, olivines are nesosilicates, meaning they consist of isolated SiO4 tetrahedrons linked by ionic bonds from interstitial cations. All members of the group crystallize in the orthorhombic system, forming a layered, closest-packed oxygen network where silicon and metal ions occupy specific tetrahedral and octahedral voids.

The group is defined by the forsterite-fayalite solid-solution series. Forsterite (Mg2SiO4) sits at the magnesium-rich end, while fayalite (Fe2SiO4) represents the iron-rich end. Most naturally occurring olivines fall somewhere in between, with their composition often expressed as a molar percentage of forsterite, such as Fo70. While magnesium-rich olivines are abundant in mafic and ultramafic igneous rocks, they are unstable in the presence of silica minerals, reacting to form orthopyroxene. Conversely, iron-rich fayalite is rarer and can exist stably alongside quartz.

Beyond Earth, olivine is a cosmic traveler. It has been identified in lunar basalts, meteorites, and the dust disks surrounding young stars. Perhaps most surprisingly, research suggests that at the extreme pressures found 360 kilometers deep within the Earth, olivine can store significant amounts of water. Because it is so prevalent, some scientists estimate that the total volume of water dissolved within mantle olivine could exceed the amount contained in all of Earth's oceans combined. This capacity to hold water drastically alters the mineral's resistance to solid flow, directly influencing the rheology of the mantle and the movement of tectonic plates.

Industrially, the high melting point and chemical resistance of magnesium-rich olivine make it a valuable refractory material for furnace linings and kilns. Whether found in the depths of the mantle, the tails of comets, or industrial smelting equipment, olivine remains a fundamental component of planetary geology.

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