This is a rather exciting time to be reviewing the topic of the thermodynamics of minerals and melts. The subject is in a state of flux. The reasons for this are both conceptual and technical and arise from the fact that the disciplines of geochemistry and petrology have now matured to recognize that equilibrium thermodynamics is inadequate for describing the mechanism of a geochemical process. To appreciate these details requires irreversible thermodynamics, or better still kinetics, and in most cases some consideration of the fluid dynamics of the system under study. These subjects build upon equilibrium thermodynamics in that adequate descriptions of the energetics of geochemical processes depend on knowing the extent to which the system deviates from the equilibrium state. In a sense this realization marks the dawning of the age of chemical affinity. To apply kinetics to geologic systems one needs excellent standard state thermodyanmic data, comprehensive solution models and large scale computational ability. Technically, research on the thermodynamics of minerals and melts has advanced (perhaps unwittingly) to meet this need in that we have seen over the last five years (1) an order‐of‐magnitude increase in the quantity and quality of thermodynamic data for silicate melts and glasses, (2) the use of spectroscopic methods to infer structural properties and thereby allow the construction of models for configurational entropies of melts and solids, and (3) the use of sophisticated computational algorithms to model multicomponent phase equilibria and extract sets of consistent thermodynamic data for geologic systems. The conceptual advances in this field have been just as revolutionary. Quantum and statistical mechanics now play their appropriate fundamental role in the description of the thermodynamic properties of geologic materials. Though we are far from the ability to predict the equation of state of a complex mineral or melt solution, it is now possible to say a great deal about the theoretical functional form of expressions describing the energetics of mixing. Let us hope this marks the close of the age of Margules parameters!
