Abstract: The infra-red spectrum and X-ray powder pattern of a chemically analysed specimen of leadhillite, a lead carbonate sulphate hydroxide mineral from Leadhills, Scotland, are shown to be different from those in the literature. The IR spectra of several specimens suggest that mutual replacement of SO₄, CO₃, and OH may occur in this mineral, and it is thought that this might be responsible for the observed variation in X-ray spacings.