Kinetics of mineral systems

Abstract

In our attempts to understand the origin and evolution of rocks, we are forced at every turn to consider the problems of kinetics. If the answers we seek are values of the thermodynamic variables of the physical and chemical environment of crystallization, we must first establish that the measurements represent equilibrium within the context of the study. The concept of equilibrium is intimately connected with the volumetric and geometric properties of the system. This arises from the universal dependence of chemical and many “physical” processes on particle diffusion. Thus the volume throughout which equilibrium is attained is always of limited size and dependent on the time scales of the events involved. This kinetic restriction on equilibrium was clearly recognized by Harker (1932), whose studies led him to conclude that generally a mineral formed at any given point within a rock depends upon the local composition within a radius of “a small fraction of an inch.” This concept of local equilibrium was referred to as mosaic equilibrium by Korzhinskii (1957). However, this term seems undesirable because it implies a certain discontinuity when we should really expect a continuous variation in the intensive variables with distance.