Petrology of metamorphic rocks

Abstract

With the appearance of Petrology of the metamorphic rocks a longstanding wish of mine has been satisfied, namely the publication of a book on metamorphic rocks designed primarily for non-specialist students interested in the Earth sciences, and which would in this way form a companion to the existing books concerned with igneous and sedimentary rocks. Individual authors necessarily approach their subjects differently not only because of their varied interests but also because of major differences in subject matter. Igneous rocks of a volcanic nature can actually be observed in the making, albeit from a respectful distance, so it has been natural that in studying igneous rocks attention has been directed very much to laboratory investigations into the crystallisation of minerals from silicate melts. Similarly, with sedimentary rocks it is generally possible to gain critical insight into their origins by observing present conditions of sedimentation and by exploration of the oceans. Metamorphic processes, however, can never be observed directly. They are largely, therefore, matters of inference from evidence provided by the rocks themselves, backed by the accumulated evidence of field studies which may be regarded as case histories relating to given sets of geological conditions and events. Since both the nature of the rocks prior to metamorphism, and the conditions to which they are subjected, vary very widely, it is impossible to do justice to all in one book, and certainly in one of an introductory nature. This is perhaps the main justification for emphasis in the present case on selected topics which have prov ed of special interest to the Author in his teaching and research experience. Certainly from my own experience there are few pursuits more exciting and rewarding than studying crystalline rocks, ideally in the field in the first instance, and then petrographically, in order to determine their nature and to interpret their histories. Fortunately this is an experience in which anyone can share who is prepared to gain acquaintance with the minerals concerned and to learn the basic rules of petrographic interpretation.