Author name: Pascal Richet

Throughout geological history, partial melting of mantle rocks and magma ascent and crystallization have played key roles in shaping the Earth. The importance of magmas stems from their liquid nature, that is, from their high atomic mobility and lack of long-range order. Compared to crystals, magmas thus have peculiar thermodynamic properties. A few examples illustrate how solid–liquid and liquid–volatile equilibria can be predicted. Given the almost infinite diversity of conditions of chemical composition, temperature and pressure in nature, thermodynamic modelling has become a necessary tool for understanding magmatic processes.

All geological changes result from the transfer of matter and energy, the study of which is the goal of thermodynamics. Investigating natural processes thus necessarily involves thermodynamic considerations. This has long been practiced implicitly, as shown by the smart reflections made by “natural philosophers” from antiquity to the 18th century about topics ranging from atmospheric phenomena to the early history of the Earth. Since the early 19th century, investigations explicitly take advantage of a rigorous framework that deals with chemical and thermal aspects of the Earth’s activity. Far from being abstruse, these principles can in fact be summarized in a simple and concise way.