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A new approach to water-rock interaction is developed which replaces the assumption of partial equilibrium with a complete calculation of the rates at which minerals form and dissolve. The evolution of reaction-flow systems towards equilibrium with respect to secondary phases is examined in terms of the important processes which generate and modify reactive surface areas of minerals: heterogeneous nucleation, crystal growth, dissolution, and crystal ripening. The widespread occurrence in surficial environments of metastable solid phases and waters supersaturated with the thermodynamically most stable minerals is attributed to the slow rates of reactive surface area generation of the latter. This is primarily because the high mineral-solution interfacial tensions of the stable minerals make it difficult to nucleate them directly. In many cases, a stable mineral circumvents direct nucleation by using as a template for its …