Olivine

nesosilicate

fayalite

Olivine is a series between forsterite Mg2SiO4 and fayalite Fe2SiO4. These are both nesosilicates (insular SiO4 groups).
Solubility: Insoluble in water, nitric and sulphuric acid; soluble in hydrochloric acid
Environments:

Plutonic igneous environments
Volcanic igneous environments
Metamorphic environments

Olivine is a common primary, rock-forming mineral, varying in amount from an accessory to a major constituent. It is the first major mineral to crystallise in the discontinuous branch of the Bowen reaction series.
Olivine is an essentail constituent of peridotite and kimberlite. It is a common constituent of gabbro, dunite, peridotite and basalt.
It also may be found in andesite, diorite, gabbro and granite.

In peridotite olivine is typically associated with chromium-rich spinel and pyroxene. Some peridotite intrusions also contain garnet, and in these the olivine is very manganese-rich (Lauf p21).

Olivine nodules are commonly found in alkaline basalt; those from shallower levels in the mantle are spinel-bearing, and those from deeper levels are garnet-bearing (Lauf p21).

Olivine can form from the progressive metamorphism of serpentinite, such as in the cascades, Washington, USA, where in the contact aureole of a granodiorite intrusion lizardite - chrysotile serpentinite was transformed first to antigorite serpentinite, then olivine serpentinite, then an assemblage of forsterite, talc and tremolite (Lauf p22).

Olivine is associated with plagioclase feldspar, pyroxene, magnetite, corundum, chromite and serpentine.
quartz never occurs with olivine.
Olivine is a mineral of the granulite facies.

Alteration

cummingtonite-grunerite and olivine to enstatite-ferrosilite and H2O
(Fe,Mg)7Si8O22(OH)2 + (Mg,Fe)2SiO4 ⇌ 9(Mg,Fe2+)SiO3 + H2O
(DHZ 2A p138)

enstatite-ferrosilite, Fe-rich diopside and Fe, Cr-rich spinel to garnet and olivine
2(Mg,Fe2+)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4
(DHZ 2A p258)

Mg-rich greenalite to olivine, Mg-rich grunerite and H2O
18(Fe2+, Mg))3Si2O5(OH)4 → 20(Fe,Mg)2SiO4 + 2(Fe2+,Mg)7Si8O22(OH)2 + 34H2O
(DHZ 1A p266)

Mg-rich greenalite to olivine, SiO2 and H2O
2(Fe2+, Mg))3Si2O5(OH)4 → 3(Fe,Mg)2SiO4 + SiO2 + 4H2O
(DHZ 1A p265)

hypersthene, augite and Fe and Cr-rich spinel to garnet and olivine
2(Mg,Fe)SiO3 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ Ca(Mg,Fe)2(Al,Cr)2(SiO4)3 + (Mg,Fe)2SiO4
(DHZ 2A p258)

olivine and CO2 to enstatite- ferrosilite and magnesite-siderite
(Mg,Fe)2SiO4 + CO2 → (Mg,Fe2+)SiO3 + (Mg,Fe)CO3
(DHZ 2A p139)

olivine and H2O to serpentine, magnetite and H2
6(Mg1.5Fe0.5)SiO4 + 7H2O → 3Mg3Si2O5(OH)4 + Fe2+Fe3+2O4 + H2
The iron Fe in olivine does not enter into the serpentine, but recrystallises as magnetite
(R&M 90.6.521).

olivine and quartz to enstatite - ferrosilite
(Mg,Fe)2SiO4 + SiO2 → 2(Mg,Fe2+)SiO3
(DHZ 2A p139)

orthopyroxene, Fe-rich diopside and Fe and Cr-rich spinel to Fe, Ca and Cr-rich pyrope and olivine
(Mg,Fe)2Si2O6 + Ca(Mg,Fe)Si2O6 + (Mg,Fe)(Al,Cr)2O4 ⇌ (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Mg,Fe)2Ca(Al,Cr)2Si3O12 + (Fe,Mg)2SiO4
The garnet-bearing peridotites are considered to have originated in a high-pressure environment according to the above reaction
(DHZ 2A p123).

Mg-rich siderite and quartz to olivine, orthopyroxene and CO2
3(Fe,Mg)(CO3)→ (Fe,Mg)2SiO4 + 2SiO2 → (Fe,Mg)2SiO4 + 3CO2
(DHZ 1A p266)

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