Magnesite

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts.

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.

It is also present within the regolith above ultramafic rocks as a secondary carbonate within soil and subsoil. Where it deposited as a consequence of dissolution of magnesium-bearing minerals by carbon dioxide within groundwaters.