An iron-sulphur coordination compound in coal has been identified for the first time. Isolation of the compound from a high sulphur Indian coal sample was performed by extracting with tetrahydrofuran followed by methanol and ultimately separated by thin layer chromatography. Characterization of the compound by proton n.m.r., i.r., u.v. and chemical analyses of iron and sulphur reveals that iron atoms are bonded to thiophenic: aliphatic and inorganic sulphur atoms. Geochemical studies have revealed that the main sources of sulphur are inorganic and sulphur amino acids mostly cysteine, cystine and methionine. Identification of the coordination compound has confirmed the nature and occurrence of secondary sulphur in coal. This compound is considered to be a new form of sulphur because it is neither purely pyritic nor organic sulphur. The discovery of the Fe-S coordination compound is a great concern for the determination of the sulphur forms in coal.