Feldspar minerals make up 60% of the crust of the Earth. They are stable in the upper mantle, and are so abundant in the crust that they form the basis of the classification of igneous rocks. At the surface, feldspars weather to form clay minerals which are the most important mineral constituent of soils. The articles in this book review the chemical reactions of feldspars over the whole sweep of pressure and temperature regimes in the outer Earth, and describe the fundamental aspects of crystal structure which underlie their properties. The book covers intracrystalline reactions, such as order-disorder transformations and exsolution, and transfer of stable and radiogenic isotopes, which can be interpreted to provide insights into the thermal history of rocks. It is suitable for final year undergraduates or research workers.

Remarks by JVS. Volumes 1 and 2 of Feldspar Minerals were published in 1974, but Volume 3 was not completed because I was forced to devote 3 years to the resolution of unforeseen problems in the construction of an ion probe. By 1977, the incomplete draft for Volume 3 had become obsolete because of the enormous advances in knowledge of feldspars, particularly those in lunar rocks and meteorites, and in both deep-seated and ancient terrestrial rocks. Furthermore, it soon became obvious that a completely new version of Feldspar Minerals was needed because of the important new results on the physical and chemical properties. I had kept up with the interesting but tedious chore of weekly reading of the incoming literature and maintenance of the files. By 1980, the intense day-to day pressure had gone from my research programs on lunar rocks and on the development of the ion microprobe as a quantitative geochemical instrument, and I began preparation of a second edition of Feldspar Minerals.

Volume 2 of Reviews in Mineralogy displays the Short Course on Feldspar Mineralogy in Salt Lake City in October 1975. The workshops on x-ray single-crystal, powder diffraction methods and electron optical techniques as applied to the study of feldspars are the substance of which became the nine chapters of the first edition of Feldspar Mineralogy. It will be noted by readers experienced with feldspars that there are many new ideas appearing in Chapters 3, 4 and 5 that have neither received scrutiny by review (other than ourselves) nor survived practical tests of time in the research community. There is some danger in this, but the editor decided the greater risk was to produce a review volume soon to be outdated. Inevitably, given the different goals of individual authors in their assigned topics, some repetition of material has occurred, although usually with quite different emphases. Chapters 1, 2, 9 and 10, in which plagioclase structures and diffraction patterns and their Al,Si distributions, phase equilibria and exsolution textures are featured, are notable in this regard.

During the past two centuries, crystallography, mineralogy and petrology have evolved from simple compilations of data to powerful disciplines based on interlocking networks of laws, hypotheses and rules-of-thumb. While many data still consist of isolated facts which defy synthesis, a gratifying portion can be organized according to physical and chemical principles. Unfortunately the separation of physical sciences into sub-divisions, especially at the teaching level, makes it difficult to integrate the different approaches to minerals. This separation is worsened by the increasing technical demands of chemical and physical theories, by the number and complexity of experimental methods, by the sheer mass of facts in an observational discipline such as mineralogy or petrology, and by the explosion of papers. This book concentrates on those aspects of the genesis and properties of feldspar minerals which can be related to physical and chemical principles. My main aim is frankly pedagogic: I wish to show how chemical and physical principles can be combined with geologic observation to produce an enhanced level of understanding of the genesis of minerals. The feldspars which demonstrate almost all of the general principles provide the most suitable example.

The Identification of Detrital Feldspars