This advanced-undergraduate and beginning-graduate text book introduces geosciences students to the fundamental principles of thermodynamics that underlie mineralogy and petrology. It is class-tested based in hysical chemistry of minerals and theoretical petrology courses, given by the author over a number of years. Thermodynamic applications to real problems are illustrated through numerous examples taken from the mineralogical literature. In this way, the more abstract nature of thermodynamics is more easily understood. The reader learns how to apply the methods of this discipline to concrete mineralogical and petrologic problems. Although written primarily for graduate students, it is also useful for advanced scientists working in the field of mineralogy, petrology and geology. It may also be interesting for ceramists and materials scientists.