The modelling of rock systems in chemical equilibrium provides one of the few quantitative links between petrology and other geoscience disciplines. Mineral equilibrium modelling may be used to estimate the pressures and temperatures recorded in igneous or metamorphic rocks, or to simulate the mineralogical changes by which a rock responds to changes in pressure, temperature, or bulk chemistry.

In this talk I will discuss some recent developments in mineral equilibrium modelling. AvPT+ is new method in geothermobarometry, implemented in the software THERMOCALC, which is in some sense a hybrid between two established methods: multiple-reaction thermobarometry and pseudosection modelling. A comparison of results from avPT+ and pseudosection modelling suggests that “just one more generation” of mineral equations of state is needed, reproducing observed mineral compositions more faithfully than the current generation. I will discuss the experiment-based approach that my research group is taking to this task, before outlining the fundamental experimental and modelling limitations on mineral equilibrium calculations.