Solid solutions: Background, history and scientific perspective
Published:January 01, 2001
The importance of solid solutions is known since prehistory times. The phrase ‘The Bronze Age’ is evidence for this and shows that mankind has for thousands of years engineered and produced materials, or taken those from nature, that consist of atomistic mixtures of elements having certain beneficial physical properties. Thus solid solutions, or mixed crystals as they are sometimes termed, are investigated in the fields of metallurgy, chemistry, physics, materials science and the Earth Science disciplines mineralogy, petrology and geochemistry. The Earth, as well as other solid planets and meteorites, is made up for the most part of minerals, largely silicates and oxides, and with the exception of some of the SiO2 phases, most are substitutional solid solutions. Silicates and oxides are quite extraordinary in their ability to incorporate many different elements and, at the same time, in having extremely large pressure and temperature stabilities. MgO and ‘FeO’ and their solid solutions are stable at ambient conditions and also at pressures and temperatures corresponding to Earth’s lower mantle. Many silicate garnets are stable at 1 atm and compositionally complex garnets are also stable in the Earth’s transition zone.
A description and understanding of the chemical and physical properties of silicates and oxides are essential for investigating geological processes. For example, most geothermobarometers that are employed on metamorphic and igneous rocks are critically dependent on the activity-compositional relationships that are used to describe the thermodynamic mixing properties of the participating solid solution phases. Existing thermodynamic mixing models for most rock-forming
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.