Metamorphism of ultramafic rocks in the presence of water and/or carbon dioxide results in two main classes of metamorphic ultramafic rock; talc carbonate and serpentinite.
Talc carbonation reactions occur in ultramafic rocks at lower greenschist through to granulite facies metamorphism when the rock in question is subjected to metamorphism and the metamorphic fluid has more than 10% molar proportion of CO2 (carbon dioxide).
When such metamorphic fluids have less than 10% molar proportion of CO2, reactions favor serpentinisation, resulting in chlorite-serpentine-amphibole type assemblages.