One of the major goals of petrology is to retrieve values of the intensive parameters, such as pressure (P), temperature (T) and fluid composition, under which the major mineralogical properties of a rock were established, along with the time scales of evolution of the mineralogical properties. The basic approach in the retrieval of the intensive properties involves comparison of the mineralogical assemblages and the mineral compositions of the rock with the phase equilibrium constraints. The latter are calculated from the internally consistent thermochemical properties of the stoichiometric end members or determined in the laboratory on relatively simple systems, usually involving only the end-member phases, and then corrected for the effects of the compositional departures as observed in a specific natural assemblage. In addition, many mineral pairs (e.g. garnet and biotite) respond to changes of P–T conditions, especially temperature, by continuous ion exchange reactions, and thus register the P–T condition or P–T history of the rock in their compositions. The ion-exchange reactions are also calibrated in the laboratory on relatively simple systems, but require corrections for the effects of additional components that enter into solid solution in the minerals in natural environments. The corrections for the compositional effects rely critically on the thermodynamic mixing properties of the components in the mineral solid solutions and fluid phase which are involved in a specific reaction (e.g. Ganguly & Saxena, 1987). There has, thus, been a sustained effort over the last few decades on the determination of thermodynamic mixing properties of phases in geologically important systems.
Figures & Tables
Solid Solutions in Silicate and Oxide Systems
The EMU book series or notes, as they are called, were introduced to provide university teachers with up-to-date reviews in important, rapidly evolving areas of mineralogy, petrology and geochemistry. They are also meant to introduce scientists into special and often interdisciplinary fields of research. In this regard, a volume on solid solutions is current and sorely needed. The solid Earth, as well as many meteorites and the other solid planets, consists for the most part of mineral solid solutions. Research on solid solutions is extremely broad encompassing work in physics and chemistry, metallurgy, materials science and, last but not least, mineralogy and petrology. Hence, because the theme is so strongly interdisciplinary in nature, the workshop was organised to include solid state physicists, physical chemists, crystallographers, mineralogists and petrologists. The various chapters reflect some of this diversity and show what mineralogy has become. Experimental investigations in mineralogy now routinely include different types of spectroscopies along with more traditional phase equilibrium, X-ray diffraction, calorimetry, and TEM methods. There have also been new and impressive developments in theory and computation. Many computational approaches relating to the study of solid solutions, for example, the Cluster Variation Method or Monte Carlo simulations, have been brought in from materials science, chemistry and physics. It can be concluded that the traditional or historical, and perhaps artificial, boundaries between the various disciplines are disappearing. Many current research efforts in mineralogy are similar to those in chemistry, materials science and physics.