The fundamental questions to be addressed by this session are 1) how properties of individual minerals affect the evolution of rocks and constrain rock-forming processes such as melting, metamorphism and metasomatic and surface alteration; 2) how relevant information on mineral behaviour can be collected and used to provide or improve thermodynamic models and their use in geosciences. Thermodynamic calculations are used to get better insight into lithosphere dynamics, to constrain melting processes in crust and mantle as well as to study fluid-rock interaction in subduction zones. The development of thermodynamic databases, accurate solid solution models as well as algorithms to determine Gibbs energy minima among a large number of rock forming minerals have made thermodynamic models an excellent tool for geodynamic, geochemical and mineralogical research. However, despite its broad application, the use and interpretation of thermodynamic models applied to natural rocks is far from being straightforward because chemical disequilibrium and/or unknown rock properties (e.g. fluid activities) complicate the application of equilibrium thermodynamics. This session will convene scientists involved in the study of major groups of rock-forming minerals and their role in petrological processes as well as in the development and applications of thermodynamic models. The session - co-sponsored by EMU - includes the 2010 EMU Medallist's talk.