Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regional metamorphic terrains. These magnesites often are cryptocrystalline and contain silica in the form of opal or chert. .Magnesite is formed via carbonation of  olivine the presence of water and carbon dioxide at elevated temperatures and high pressures typical of the greenschist facies.

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