Thermodynamics is crucial for understanding the conditions under which natural geomaterials equilibrate, helping to determine equilibrium pressures, temperatures, and the chemical composition of phases involved in mineralogical and petrological processes. Laboratory studies often focus on simple chemical model systems with few components to gain insights into more complex natural systems. To apply phase equilibrium results from these models to natural geologic materials, extrapolations in compositional space and varying pressure-temperature (P-T) conditions are necessary, achievable through thermodynamic mathematical formalism. While numerous excellent books on thermodynamics in mineralogy, petrology, and geochemistry have been published over the last 40 years, many target advanced students and researchers, assuming prior knowledge of the subject. This often leaves basic concepts insufficiently addressed for beginners. The aim here is to present the fundamental principles of thermodynamics at an introductory level while maintaining the mathematical rigor that is essential to the field. This approach seeks to bridge the gap for those new to thermodynamics, providing a solid foundation for further study.
