Metamorphic petrology is the study of solid-state, physical, and chemical changes that take place within the crust of the Earth and other planets. The major tool of modern petrologists is equilibrium thermodynamics, which allows prediction of the mineral assemblages that are likely to be stable at a given pressure and temperature, or conversely, to estimate pressure and temperature of equilibration for given mineral assemblages.

Nonequilibrium thermodynamics can be used to study a different set of conditions: metamorphic textures or zoning patterns in minerals, features that form from the interplay of diffusion, nucleation, kinetics, surface, and strain energies. This method is used to determine whether an assemblage formed at peak temperature or during retrogression and to monitor the pressure-temperature history of a rock.