Secondary alteration of rocks and their contained minerals is common in nature. Alteration reflects the interaction of fluid, typically dominated by water, with rock at temperatures that range from warm (< 100°C) to hot (>500°C). For geologists who wish to study the primary mineralogy and chemistry of rocks, alteration is a nuisance to be avoided. Alteration mineralogy, however, documents the post-formation history of the rock, information that has practical implications. In particular, alteration is ubiquitous in and around hydrothermal mineral deposits. The distribution and mineralogy of this alteration relates to the hydrothermal environment, and hence, the type of mineral deposit. More importantly for mineral exploration, hydrothermal alteration around mineral deposits commonly forms halos that provide a target which is much larger than the deposit itself. The mineralogy and in some environments the chemical composition of the alteration provide an indication of the proximity of mineralization, or in the ideal case, a vector towards mineralization. Interpretation of alteration is, therefore, a routine part of exploration for hydrothermal mineral deposits. Similarly, as a product of geothermal activity, the mineralogy of hydrothermal alteration provides information on reservoir and fluid characteristics, and the evolution of the geothermal system. These data are used in conjunction with other information to evaluate potential geothermal resources.

Our knowledge of metamorphic and deformational rock fabrics has been acquired largely by studying the products of deformation in ancient fold belts. As such, our understanding of how rock fabrics form has been built up from inferences about, rather than direct observations of, processes that might have operated, and many of those inferences have proved incorrect.

Atlas of igneous rocks and their textures A companion volume to the Atlas of Rock-forming Minerals in Thin Section, this full-colour handbook is designed to be used as a laboratory manual both by elementary students of earth sciences undertaking a study of igneous rocks in thin section under the microscope, and by more advanced students and teachers as a reference work. The book is divided into two parts — Part One is devoted to photographs of many of the common textures found in igneous rocks with brief descriptions accompanying each photograph. Part Two illustrates the appearance of examples of some sixty of the commonest (and a few not so common) igneous rock types; each photograph is accompanied by a brief description of the field of view shown. Nearly 300 full-colour photographs are included, and in many cases the same view is shown both in plane-polarized light and under crossed polars. A brief account of how thin sections can be prepared is included as an appendix. It is believed that the amateur geologist using these instructions will be able to make his own thin sections and, with the aid of a relatively simple microscope, enjoy the study of rocks in thin section.

Migmatites are spectacular, complex-looking rocks that can inspire, fascinate, or confuse geologists. All migmatites viewed in an outcrop represent the sum of a series of processes that acted in parallel, or sequentially, and the influence of various local factors (see the photographs in section A). In order to begin to understand the complexity and seemingly endless variety in migmatites, and to provide the reader context for the subject of this book, some of the key factors and processes that make individual migmatites the way they are should be outlined at the outset <...>