The structure of Pb 5Sb 6S 14, first observed by HREM, has been refined by single crystal X-ray diffraction. It is a higher homologue of robinsonite, Pb 4Sb 6S 13, with a = 28.367(8) Å, b = 4.024(1) Å, c = 22.044(7) Å, α = 89.59(2), β = 92.28(3), γ = 89.93(2), space group I overline1, Z = 4 . Pb 5Sb 6S 14 is built from two different ribbons composed of square pyramidal (Pb, Sb)S 5 groups with the narrow ribbon identical to that in robinsonite and the other ribbon one pyramid wider. HREM studies indicate that during electron microscope observation Pb 5Sb 6S 14 decomposes into three different polymorphs of PbS. High resolution electron micrographs allow models to be proposed for the transformations.