Structures of the pseudo-trigonal polymorphs of Cu2(OH)3Cl

The crystal structure of Cu-2(OH)(3)Cl has been determined using two natural samples with almost ideal stoichiometry. While one of the samples exhibits a twinned clinoatacamite structure, the other sample is characterized by the appearance of additional weak diffraction maxima at half integer positions of h and k. Structure refinement was carried out with the space group P(1)overbar. The relationship between the triclinic phase, clinoatacamite, paratacamite and the herbertsmithite structure is discussed in terms of symmetry as a function of Cu concentration.