Iron III sulfate hydrate; Fe2(SO4)3xH2O; Molar mass 399.88 g/mol Also known as ferric sulfate, ferric sulphate. It is a chemical compound, a rhombic crystalline salt. Manufactured on a large scale for use in the dyeing process as a mordant, it helps to fix the dye in the fabric. It is used as a medical astringent and styptic as well as a coagulant for industrial wastes. The Mars rover, Spirit, was lost when it became stuck in an iron III sulphate deposit.