Metamorphic Crystallization investigates the upper regions of the crystalline Earth, where countless solid-state chemical changes have taken place during the long history of the planet. The exploration proceeds in five stages. Firstly, a brief reminder of the importance of field, microscopic, and experimental phase-equilibrium results in metamorphic studies is given, followed by a review of classical thermodynamics as applied to minerals. Different kinds of mineral equilibria are defined, and representative natural and experimental examples of each kind are examined. The kinetics of reactions involving crystals (reaction rate, diffusion, nucleation, crystal growth), referring to certain experiments that have provided information on these microprocesses, are reviewed. Finally, the granular microstructure of natural samples (crystal shape, size, spatial distribution) together with chemical data are examined, and an interpretation of these observations in terms of mineral kinetics is pursued. This exploration intends to leave the reader more appreciative of changes which occur within the Earth, and more interested in the application of thermodynamics and kinetics in the study of these changes.