Clays presents the fundamentals of the mineralogy and geology of clays through clear explanations of the mineralogical and geological problems involving clay minerals. It first introduces key concepts (crystallography and mineralogy of clays, thermodynamics, isotope chemistry, surface physical properties), setting the stage for readers to learn how clay minerals are formed or transformed in the principal geological environments at the Earth's surface. Abundant illustrations, short paragraphs, exercises and applications support the comprehension of key concepts underlying crystallography, chemical reactions and geological situations. Theoretical demonstrations are reduced to the minimum necessary to grasp the fundamentals. Aimed for graduate students and scientists (geologists, geographers, engineers, environmental and soil scientists), Clays provides a comprehensive introduction to an important geological topic.