Talc carbonates are a suite of rock and mineral compositions found in metamorphosed ultramafic rocks.

The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions: talc and the carbonate mineral magnesite.

Talc carbonate mineral assemblages are controlled by temperature and pressure of metamorphism and the partial pressure of carbon dioxide within metamorphic fluids, as well as by the composition of the host rock.

In a general sense, talc carbonate metamorphic assemblages are diagnostic of the magnesium content of the ultramafic protolith.

Thus, the MgO content of a metamorphosed ultramafic rock can be estimated by understanding the mineral assemblage of the rock. Magnesium content determines the proportion of talc and/or magnesite and aluminium-calcium-sodium content determines the proportion of amphibole and/or chlorite.

Several minerals are diagnostic of talc carbonated ultramafic rocks;

At amphibolite facies, the diopside-in isograd is reached (dependent on carbon dioxide partial pressure) and metamorphic assemblages trend toward talc-pyroxene and eventually toward metamorphic olivine.

Serpentinisation of olivine: