The book provides a practical handbook for identifying rock-forming minerals under the microscope by presenting essential optical theory, descriptions of petrographic microscope components, and step-by-step investigation techniques. It explains light behavior in crystals, methods for measuring refractive indices and birefringence (including Becke and van der Kolk procedures), interpretation of pleochroism, interference colors, extinction angles and interference figures, and criteria for distinguishing crystal systems. Individual minerals are described by their microscopic characters and typical appearances in thin section. Chapters also cover preparing and mounting thin sections, useful tables and diagrams, and simple chemical and mechanical tests.