Crystalline Solutions and Geothermometry

Abstract

The concept of metamorphic facies evolved through the attempts of the petrologists to distinguish the mineral assemblages formed at different P and T in the field. In several cases, the physical and chemical conditions of the formation of rocks have been simulated in the laboratory. However, the meagerness of relevant thermodynamic data on rock-forming minerals makes it difficult to interpret meaningfully and check the validity of most experiments. From existing knowledge, it is possible to obtain only certain qualitative to semiquantitative estimates of P and T of the formation of a mineral assemblage. Such methods are based on the knowledge of the chemical reactions that occur as a result of changing P and T within and in between the crystalline solutions.