What is MC_fit?

• It is a Perple_X computer program based on the algorithm of Khan et al. [Khan2021] for inverting natural and experimental phase equilibria for thermobarometric conditions and/or unknown thermodynamic parameters [Pitsch2025].

• It works by finding the best match between observations and a thermodynamic model of the observations predicted by free energy minimization as a function of any unknown parameters.

• It can propagate both analytical and thermodynamic parameter uncertainties to estimate the uncertainty of the inversion parameters.

• It does not require complete compositional information; it can invert for unmeasured properties such as ferric-ferrous ratio and volatile content.

• It can incorporate, but does not require, knowledge of the bulk composition of the system and information on phase proportions.

The use of MC_fit for thermobarometric problems is documented here.