2 Fe₂S₃^-II + 9 O₂⁰ → 2 Fe₂O₃^-II + 6 S^IVO₂^-II

This is an oxidation-reduction (redox) reaction:

6 S^-II - 36 e^- → 6 S^IV (oxidation)

18 O⁰ + 36 e^- → 18 O^-II (reduction)

Fe₂S₃ is a reducing agent, O₂ is an oxidizing agent.