It is often necessary to determine whether or not a metamorphic mineral assemblage contains a reaction relationship; is so, the assemblage cannot represent an equilibrium state. Similarly, it is often necessary to determine whether two assemblages, each apparently in equilibrium, define a mutual reaction relationship; if so, they cannot have equilibrated under the same conditions. This work will be a study of special mathematical techniques to analyse metamorphic assemblages and reactions, will prepare a set of computer programs for the use of the petrological community, and will test the techniques developed on mineral assemblages in pelitic schists. It should provide a new and better means for geologists to determine the conditions under which metamorphic rocks formed, and hence what was going on at a given time in the crust of the earth.
