Mineral assemblages of igneous and metamorphic rocks may reflect the approach of a rock to the equilibrium during its formation. The accurate measurements of the thermodynamic properties of minerals, melts and volatile fluid phases, combined with experimental and theoretical studies of their mixing properties, have made it possible to calculate the equilibrium conditions for particular rock systems. The equilibrium thermodynamics provides a way of looking at rocks, not only for discovering at what conditions they formed, for example the temperature and pressure of formation, but also for...