Abstract: The rare iron-tin hydroxide minerals natanite and jeanbandyite occur as small pseudo-octahedral crystals in high-temperature Sn-Cu-As veins at Penberthy Croft Mine and Hingston Downs Quarry, Cornwall. The lattice parameters for jeanbandyite and natanite are reported and compared to previously calculated values. The chemical composition of jeanbandyite is discussed and a significant proportion of divalent Fe and Mn is shown to be present.