Fig. 5: Sample evidence and thermodynamic calculations of the by-products of the oldhamite formation reaction.

a HAADF and EDS mapping of the Fe and S-rich region near oldhamite in impact glass (Oldhamite is labeled as Oldh; the solid yellow line indicates the Oldh area, and the white circles indicate the Fe- and S-rich region; in EDS-mapping, green is Ca, pink is Fe, and yellow is S); b Gibbs free energy criterion for possible reactions of characteristic products in oldhamite system (The blue curve and purple curve are the Gibbs free energies corresponding to different chemical reactions, and the pink background and blue background are the areas where the Gibbs free energy is greater than and less than 0, respectively.); c Thermochemical equilibrium calculation of S element with gradual addition of Ca²⁺ ions in the system (The curves corresponding to the fonts of different colors represent the physical phases of the S element distribution.).