Structures of the pseudo-trigonal polymorphs ofCu_2(OH)_3Cl

摘要

The crystal structure of Cu_2(OH)_3Cl has been determined using two natural samples with almost ideal stoichiometry.While one of the samples exhibits a twinned clinoatacamitestructure, the other sample is characterized by the appearanceof additional weak diffraction maxima at half integer positionsof h and k. Structure refinement was carried out with the spacegroup P1. The relationship between the triclinic phase,clinoatacamite, paratacamite and the herbertsmithite struc-ture is discussed in terms of symmetry as a function of Cuconcentration.