The crystal structure and composition of the mineral creaseyite from Iquique, Chile has been studied using X-ray single crystal diffraction and electron microprobe analysis. The needle like, pale green crystals are elongated parallel [001]. An idealized composition Pb2Cu2Fe23+(Si4.667Al0.333)O15.333(OH)3 · H2O has been obtained by crystal structure analysis. Creaseyite is orthorhombic, space group Cmcm, a = 12.502(8), b = 21.402(11), c = 7.303(6) Å. It exhibits substantial disorder of Si, Al and their oxygen ligands along [001]. Pb2+ occurs in a strongly asymmetric coordination, imposed by its lone pair electrons. Creaseyite is nanoporous, forming open channels of elliptical cross section along [001]. In the untreated crystals the channels are occupied by water molecules in an off-centred position. The lone pair electrons of Pb2+ extend into the channels. It is expected that the lone pair electrons are accessible to small acceptor molecules or polarizable atoms substituting for water as the extra framework constituent.