The format of mineral description has undergone considerable evolution in recent years. New illustration have been subtituted to call attention to improved equipment now available. Pahse microscopy is illustrated. The cahpter intened to guide the student in the selection of methods of grinding thin sections has been revised. A cahpter is included to serve as an outline in acquiring a working knowledge of the universal stage. The identivication tables have been revised in an attempt to make them more useful in the solution of the problem of identiying unknow minerals. The text is inteded primarly for thin-section study, but both the descriptions and the tables will be found useful for work with mineral fragments. The feldspars have been the subject of considerable revision in the light of recent studies. Other mineral groups have not been so extensively revised, although frequent revision will be noted throughout. This applies to the pyroxenes, amphiboles, chlorite, serpentine, the clays, and evaporites.