Magnetic desulfurization is an attractive physical method of coal cleaning which has been studied for a quarter century. High‐frequency selective heating of coal to convert nonmagnetic pyrite to moderately magnetic pyrrhotite has been suggested to enhance separation. Despite predicted feasibility, some successes have only recently been attained. We report on the use of Mo¨ssbauer spectroscopy and magnetization to follow indirectly the amounts of inorganic sulfur in coal. We observe significant conversion (≳10%) to pyrrhotite by microwave treatment of coarse coal granules at 915 MHz and 2.45 GHz at power levels of a few kW for about 1 min. Analysis of phase distribution allows independent calculation of the inorganic desulfurization resulting from microwave treatment and magnetic separation.