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LITHOEN

Mineral

Forsterite

The magnesium end member of the olivine series and the dominant mineral of the upper mantle. Its structure is isolated silicate tetrahedra bound by magnesium and iron, which is why its composition varies continuously toward the iron end member.

A stacked diagram with chemical element at the base, mineral species above it, mineral group to the side, and rock at the top, with a separate boxed note that ore, commodity and resource are not implied by any of them.
SchematicFour different kinds of thing that ordinary usage runs together. An element is defined by atomic number; a mineral species by structure and composition, and accepted by name; a mineral group gathers species and is not itself a species; a rock is an aggregate of minerals. None of these levels implies an ore, a commodity or a resource.
Full description of this figure

Reading upward: chemical elements, defined by atomic number, with silicon, oxygen, magnesium and iron as examples. Above them, mineral species — naturally occurring, ordered in structure, with a characteristic composition, and accepted under that name by the International Mineralogical Association — with forsterite as an example. Beside them, mineral groups and series, which gather species and are explicitly not species themselves, with olivine as an example. Above, rocks, which are aggregates of one or more minerals, with peridotite as an example. Set apart in a bordered box: ore, commodity and resource, none of which follows from any level below.

Original Lithoen diagram · LITHOEN-ORIGINAL

Classification

formula
Mg2(SiO4)
ima status
grandfathered
crystal system
orthorhombic

How this record is known

5
Settled consensus
Cited as the accepted position of the discipline.

5 of 5 claims on this page cite at least one registered source. Counts describe how each statement is known, not how likely it is to be true.

What Lithoen records

Each claim states how it is known and cites its evidence.

EstablishedApproved formulas are idealised; natural compositions vary by substitution.

An approved formula is an idealised composition. Natural crystals of most species depart from it by substitution, so a single fixed formula describes a species rather than any particular sample of it.

  • precision note: The IMA list gives some formulas with explicitly variable cations, such as augite’s (Ca,Mg,Fe)2Si2O6, which is the list acknowledging the same point.

Evidence support: Supported by the cited evidence 3 sources, multiple sources, independence unknown

Evidence: Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association 2026 Primary authority; Mineral Data Publishing 2001 Institutional reference; Mineral Data Publishing 2001 Institutional reference

EstablishedOrthorhombic

The Handbook of Mineralogy records the crystal data of forsterite as orthorhombic.

Evidence support: Supported by the cited evidence one source

Evidence: Mineral Data Publishing 2001 Institutional reference

Established3.275 g/cm3

The Handbook of Mineralogy gives a measured density for forsterite of 3.275 g/cm3.

  • precision note: A reference value from a compiled data sheet, and for several species the midpoint or single figure of a published range.
  • method: Compiled from published measurements; Lithoen holds no measurement of its own.

Evidence support: Supported by the cited evidence one source

Evidence: Mineral Data Publishing 2001 Institutional reference

Established7 on the Mohs scale

Forsterite has a Mohs hardness of 7, the same nominal hardness as quartz.

  • precision note: Mohs hardness is an ordinal scale of scratch resistance, not a measured physical quantity on a ratio scale.

Evidence support: Supported by the cited evidence one source

Evidence: Mineral Data Publishing 2001 Institutional reference

EstablishedMg2(SiO4)

Forsterite is an accepted mineral species in the IMA List of Minerals, with the CNMNC-approved formula Mg2(SiO4) and IMA status “grandfathered”.

  • definition basis: IMA List of Minerals, September 2026 update, which is the authority on mineral species status.
  • precision note: An approved formula is an idealised composition; natural crystals of most species depart from it through substitution.

Evidence support: Supported by the cited evidence one source

Evidence: Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association 2026 Primary authority

In the knowledge graph

Figures

A schematic with a crystal on the left containing sized lattice sites, a melt on the right, arrows exchanging ions between them, and the definition of the partition coefficient D as concentration in crystal divided by concentration in melt.
SchematicWhether an element enters a growing crystal or stays in the melt depends on how well its charge and radius fit the lattice site on offer. The partition coefficient D expresses that as a ratio — but it is a ratio for one cation, one site and one set of conditions, not a property of the element.
Full description of this figure

On the left, a crystal is drawn with three lattice sites of fixed size, each holding a cation. A cation whose charge and radius fit a site is taken into the crystal and is called compatible, with a partition coefficient greater than one. On the right, a melt is drawn as a disordered field able to accommodate cations of any size; a cation that fits the crystal sites poorly is left there and is called incompatible, with a partition coefficient below one. Arrows run in both directions between the two. The partition coefficient D is defined as the concentration in the crystal divided by the concentration in the melt. The figure is labelled schematic and carries the caution that compatibility is a property of a cation in a particular site under particular conditions.

Original Lithoen diagram · LITHOEN-ORIGINAL

A translucent olive-green forsterite crystal on a light background.
A forsterite crystal specimen. Forsterite is the magnesium end member of the olivine series and the dominant mineral of the upper mantle; natural olivines sit somewhere between it and the iron end member, fayalite.

Robert M. Lavinsky, CC BY-SA 3.0 · CC-BY-SA-3.0 · source · Derivative: Downscaled to 1000 px wide by the Wikimedia thumbnail service; no cropping, no colour or content alteration.

A rounded pale-green granular nodule set within dark grey fine-grained basalt.
An olivine-rich nodule enclosed in basalt, from Smrčí, Czech Republic. Nodules like this are fragments of mantle rock carried upward by erupting magma, which is why they matter: they are among the few pieces of the mantle that can be held. Locality: Smrčí, Czech Republic.

Zbynek Burival, CC BY-SA 4.0 · CC-BY-SA-4.0 · source · Derivative: Downscaled to 1200 px wide by the Wikimedia thumbnail service; no cropping, no colour or content alteration.

Five groups of triangles representing silicon-oxygen tetrahedra, arranged as isolated units, a single chain, a double chain, a sheet and a framework, each labelled with example minerals and a silicon-to-oxygen ratio.
SchematicHow silicon–oxygen tetrahedra link, and what each arrangement produces. Sharing more oxygens between tetrahedra lowers the oxygen content relative to silicon, from 1:4 in isolated tetrahedra to 1:2 in a framework — which is why the structural class can be read from the formula.
Full description of this figure

The diagram sets out five structural classes of silicate. Isolated tetrahedra share no oxygens and give Si:O of 1:4, as in olivine and garnet. Single chains share two oxygens per tetrahedron, giving 1:3, as in pyroxene. Double chains share two and three alternately, giving 4:11, as in amphibole. Sheets share three, giving 2:5, as in mica and clay. Frameworks share all four, giving 1:2, as in quartz and feldspar. Moving left to right is a progression of increasing polymerisation.

Original Lithoen diagram · LITHOEN-ORIGINAL

Record last updated 2026-09-06. Corrections follow the published corrections policy; superseded claims are retained, never silently edited.