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Material World
Mineral · (Mg,Fe)2SiO4

Olivine

The green magnesium-iron silicate that makes up most of the upper mantle — the most abundant mineral inside the Earth.

Gemstone Refractory

Olivine is not a single mineral but a continuous solid solution between forsterite, the magnesium end, and fayalite, the iron end, with every composition in between occurring naturally. That is why its density is quoted as a range rather than a figure: the range is the mineral, not measurement scatter.

It matters because of where it is. Olivine makes up most of the Earth's upper mantle, which makes it the most abundant mineral in the planet even though it is only modestly common at the surface. What reaches the surface arrives as fragments carried up by volcanic eruptions or as slabs of mantle rock thrust into place by tectonics.

How it forms

Olivine crystallises first from cooling basaltic magma, at higher temperatures than almost anything else in the melt, which is why it settles out and accumulates at the base of magma chambers to form the rock dunite.

It is also the least stable common silicate at the surface. Water attacks it readily, converting it to serpentine and releasing magnesium — a reaction so favourable that it is being pursued deliberately as a carbon capture route, because the magnesium liberated will bind carbon dioxide as solid carbonate.

How to identify it

Olive green, glassy, and occurring as rounded granular masses rather than well-formed crystals in most rocks. The colour deepens toward brown as iron content rises, and the magnesium-rich compositions are the pale bright greens sold as peridot.

It is harder than glass and shows no good cleavage, breaking in curved conchoidal fractures. In a dark igneous rock, scattered green glassy grains that resist scratching with a knife are almost always olivine — pyroxene, its usual companion, is darker and cleaves in two directions at close to right angles.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is a component of

  • Basalt — rock · an early-crystallising constituent of basaltic magma
  • Kimberlite — rock · 40–70% · the mineral the rock is mostly made of, generally altered to serpentine near the surface
  • Peridotite — rock · 40–90% · the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition
  • Gabbro — rock · in the olivine gabbros, and abundant in the lower layers of a layered intrusion

contains

  • Magnesium — element
  • Silicon — element
  • Iron — element · substitutes within a solid solution — an individual specimen may hold little of it
  • Oxygen — element

is commonly confused with

  • Quartz — mineral · both glassy and hard, but olivine is green and granular where quartz is colourless and forms prisms

is used as

  • Refractory lining — application · foundry sand and furnace lining — high melting point, low reactivity with molten metal

includes

  • Forsterite — mineral · the magnesium end member Wikidata
  • Fayalite — mineral · the iron end member Wikidata

has variety

  • Peridot — mineral variety · gem-quality olivine, and the iron that colours it is part of the essential composition rather than an impurity — which is why there is only one colour of peridot

Sources

  • Material World
    Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Olivine back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Downstream — what it becomes

  • Olivine → is a component of (an early-crystallising constituent of basaltic magma) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (quarried rather than mined, and the distinction is legal and technical rather than merely a word) → Mining and quarrying → is associated with (steam pumping allowed mines below the water table, which is what made deep coal possible) → Industrial Revolution complete chain
  • Olivine → is a component of (in the olivine gabbros, and abundant in the lower layers of a layered intrusion) → Gabbro → is an input to (for the dark polished cladding and memorials sold as black granite) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (quarried rather than mined, and the distinction is legal and technical rather than merely a word) → Mining and quarrying → is associated with (steam pumping allowed mines below the water table, which is what made deep coal possible) → Industrial Revolution complete chain
  • Olivine → is a component of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Peridotite → is a source for (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (cladding, flooring, kerbs and monuments) → Construction
  • Olivine → is used as (foundry sand and furnace lining — high melting point, low reactivity with molten metal) → Refractory lining
  • Olivine → is a component of (the mineral the rock is mostly made of, generally altered to serpentine near the surface) → Kimberlite
  • Olivine → is a component of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Peridotite → is a source for (serpentinite is hydrated peridotite; the protolith is the mantle rock itself) → Serpentinite → is a source for (chrysotile is serpentine that crystallised across an opening crack, which is why it occurs as cross-fibre veins and why serpentinite hosts most of what was ever mined) → Asbestos

These are the most distinct paths onward. Olivine ends up in others besides.