Mineral behaviour at extreme conditions
Extreme conditions and their effects on matter and materials are currently fashionable topics in modern science. Perhaps the fascination derives from the unimaginable dimensions that grab our attention and push the boundaries of our imagination. Imagine the pressures in extremely dense neutron stars where electrons and protons are fused together and atoms collapse to the density of an atomic nucleus; imagine temperatures of thousands of degrees Kelvin at the solar surface, or multimegabar and terapascal pressures deep within the interior of our planets. But even a simple droplet of water represents an extreme environment when it comes into contact with an otherwise stable crystal of rock salt, causing the crystal to dissolve as external conditions are drastically changed. We have an inherent desire to understand these diverse kinds of phenomena in nature, the mechanisms of the material changes involved, as well as the extreme conditions which are becoming increasingly demanded to achieve the extraordinary performance of new engineering materials. This rapidly evolving area of science is necessarily interdisciplinary, as it combines fundamental physics, chemistry and biology with geoplanetary and materials science, in addition to increasingly becoming one of the keys to engineering and technology aimed at process optimisation. Current experimental methods permit materials to be studied at pressures of several megabars, temperatures of tens of thousands of degrees Kelvin, and to achieve magnetic fields of several thousand teslas. Moreover, the rapid surge in computer technology has, in turn, permitted the solution of many previously intractable problems, and now even allows the behaviour of matter to be predicted far beyond the range of conditions currently accessible to experimentation. Previously unknown phenomena such as the formation of new phases, new forms of electronic and magnetic order, melting, atomic and electronic excitation, ionisation or the formation of a plasma state might result from exposing matter to extreme conditions well beyond those which were characteristic of the equilibria at the time of formation. With this volume of EMU Notes in Mineralogy we have endeavoured to provide up-to-date reviews of our understanding of the behaviour of minerals and geomaterials at exterior conditions that are sufficiently extreme to induce changes. In total 18 chapters reflect the diversity of this theme, but also demonstrate how strongly interdisciplinary this domain of modern mineralogy has become, bringing together physicists, chemists and geologists as well as experimentalists and computer scientists. The present volume contains the contributions of the lectures presented at the 7th EMU School, held at the University of Heidelberg from June 19 to June 25, 2005.
Mineral surfaces - Part II: Structure and reactivity
Published:January 01, 2005
Humanity has a long history of curiosity about the solids of the Earth and applying them as objects of beauty, wealth, power and practical advantage. From the first use of a stone tool, through the bronze age, iron age, the time of the alchemists, the ageof coal, steam and steel and now the silicon age, we have exploited minerals and shaped them to our purposes. For a couple of centuries, analytical tools have allowed us to identify mine-rals and describe their physical and chemical properties, so their bulkcomposition and structure are reasonably well characterised. Likewise, methods have been available for defining the compositionofsolutions and gases. Interactions between solids and fluids have been explored and conceptual models have been proposed for how atoms come to and leave surfaces, but only recently have we been able to confirm or disprove these models through direct observation at the molecular scale. It is the reactions that take place at the interface between phases that determine the properties of them both. An understanding of the mechanisms responsible offers scientists a powerful tool in pre-dicting the behaviour of the natural world and in engineering materials that continue to suit our purposes.
Whether Earth scientists are interested in the crystallisation of a melt in a magma chamber, or the recrystallisation that results in a diagenetic cement in a sandstone, or the accumulation of precious elements to form an ore deposit, or a hydrocarbon reservoir, or in the wide dispersal of contaminants throughout environmental systems, or the uptake or release of gases by a soil ora subduction zone, the chemical processes are the same.