Robin Gill, of the Department of Earth Sciences, of the Royal Holloway, University of London released his(her) text prepared in 2010 to the Internet. This book has grown from her experiences teaching a second - year igneous petrology course at Royal Holloway, University of London. At this intermediate level, one’s primary goal is to help students to develop appropriate descriptive and interpretive techniques. An emphasis on skills dictates a different order of priorities to those that one would embrace in writing a book on petrogenesis. Faced with an intermediate rock of unknown provenance, a student should be encouraged to describe objectively the rock that they see, and to infer what they can from this information, rather than bend their analysis to fit a pre- conceived name, origin or tectonic association.
The term ‘andesite' should emerge from the student’s examination, on the basis of the mineralogy they observe or the chemical data they are presented with, not because they happen to know that the rock comes from Japan (useful hint though that might be). Therefore, as he (she) sees it, the book that students need at this stage is one that can help them translate a set of observations (e.g. ‘a rock consisting of abundant plagioclase and hornblende phenocrysts set in a fine-grained groundmass, mainly consisting of intermediate plagioclase + augite + opaques’ ) into an informative, appropriate name (‘plagioclase - hornblende - phyric andesite’ – see Chapter 6 ). Intermediate students also need guidance in interpreting textures and geochemical data intelligently for themselves, in order to draw informed conclusions about magmatic processes.
To support this practical student-led emphasis, most chapters in the book are devoted to major rock families (basalts, gabbroic rocks, granitic rocks, etc.); geotectonic environments are of course discussed, but they do not determine the structure of the book as they might in a text emphasizing magma genesis. Once the nuts and bolts of igneous nomenclature have been introduced in Chapter 1, the order of chapters reflects a logical journey from the simplest, most abundant, least fractionated products of mantle melting (basalts, Chapter 2 ) and their plutonic equivalents (Chapters 4 and 5 ), through to more evolved magma types in Chapters 6and 8.
The final chapter examines the alkali rocks, whose diversity and mineralogical complexity challenge even the most dedicated student! Chapters 3 and 7 digress, at the points in the book where this is most pertinent, to examine experimental petrology (an invaluable laboratory window on magma evolution) and concepts of physical volcanology.
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