The feldspars form the most abundant group of minerals in the crust of the Earth and Moon and also occur in many meteo rites. They playa fundamental role in all rock-forming processes at shallow depths, but are rare or absent from the upper mantle. Their detailed study is thus essential for the understan ding of such varied processes as magma genesis and differentia tion, metamorphism, al teration, erosion and sedimentation. This interest is show by the fact that two previous NATO Advanced Study Institutes on feldspars were held in Oslo in 1962 and in Manchester in 1972. The feldspars are particularly sui table for detailed studies, as they have very simple chemistry and develop some of the most complex microstructures known. The microstructures are often slow to form but are easily preserved, so that they are potentially extremely informative about the geological history of the rocks in which they occur. Furthermore, their study involves physical and chemical methods of increasing sophistication so that the results obtained are not always immediately understandable to research workers outside the field of modern mineralogy. Progress in knowledge about feldspars is probably slower in penetrating the fields of petrology and geochemistry than that on other mineral groups. For these reasons among others, i was particularly appropriate to hold a third NATO ASI on feldspars approximately ten years after the last one."

The feldspars form the most abundant group of minerals in the crust of the Earth and Moon and also occur in many meteo rites. They playa fundamental role in all rock-forming processes at shallow depths, but are rare or absent from the upper mantle. Their detailed study is thus essential for the understan ding of such varied processes as magma genesis and differentia tion, metamorphism, al teration, erosion and sedimentation. This interest is show by the fact that two previous NATO Advanced Study Institutes on feldspars were held in Oslo in 1962 and in Manchester in 1972. The feldspars are particularly sui table for detailed studies, as they have very simple chemistry and develop some of the most complex microstructures known. The microstructures are often slow to form but are easily preserved, so that they are potentially extremely informative about the geological history of the rocks in which they occur. Furthermore, their study involves physical and chemical methods of increasing sophistication so that the results obtained are not always immediately understandable to research workers outside the field of modern mineralogy. Progress in knowledge about feldspars is probably slower in penetrating the fields of petrology and geochemistry than that on other mineral groups. For these reasons among others, i was particularly appropriate to hold a third NATO ASI on feldspars approximately ten years after the last one."

One of the fundamental objectives of physical geochemistry is to understand the evolution of geochemical systems from microscopic to regional and global scales. At present there seems to be a general recognition of the fact that internal properties of minerals record important aspects of the evolutionary history of their host rocks which may be unraveled by very fine scale observations. A major focus in the development of geochemical research in the last thirty years has been the application of classical thermodynamics to reconstruct the conditions at which the states of quenched mineralogical properties of rocks have equilibrated during the course of their evolution. While these works have funda mentally influenced our understanding ofthe physico-chemical history ofrocks, in recent years petrologists, mineralogists, and geochemists have been making greater efforts towards the application of kinetic theories in order to develop a better appreciation of the temporal details of geochemical processes. The present volume brings together a variety of current research on transport in systems of geochemical interest from atomic to outcrop scales. A major theme is atomic migration or diffusion, and its various manifestations on microscopic and macroscopic scales. Transport in the solid state is controlled by diffusion and is responsible for the states of atomic ordering and relaxation of composi tional zoning in minerals, development of compositional zoning during cooling, exsolution lamellae, and creep."