This repository contains data, code, figure files, and supplementary materials supporting the manuscript “A thermodynamic–kinetic approach to equilibrium and quench speciation of volcanic mercury”. The archive includes reduced NIST-JANAF-based halide control calculations, equilibrium speciation outputs, quench diagnostics in log-activity-ratio space, sulfide saturation sensitivity outputs, figure-ready files, and the Python workflow used to reproduce the numerical figures and diagnostic tables. The repository is intended to provide an auditable computational record for the thermodynamic–kinetic construction of equilibrium and quench speciation diagrams for mercury-bearing volcanic gases.