Coal from two seams in Eastern Canada was pyrolysed at temperatures up to 532°C and at pressures of 50 torr or atmospheric. Selected sulphide occurrences in polished sections of the chars were examined for completeness of the transformation to “FeS” with the use of quantitative scanning electron microscopy. Results showed that porous framboidal aggregates reacted at temperatures 100°C lower than monolithic occurrences. In addition, low pressure pyrolysis reduced the reactivity of sulphide, and it is suggested that marcasite reacted more readily than pyrite. The relevance of these findings to the removal of sulphur from coal by magnetic beneficiation is discussed.