Buttgenbachite from Cornwall : a single-crystal X-ray study

A single crystal X-ray structure of a supposed connellite specimen originally from the collection of N. Story-Maskelyne, Cornwall (Natural History Museum specimen BM 1951,455) has shown that the crystal examined is in fact buttgenbachite. There is no evidence for the presence of any sulphate in the lattice. The origin site is partially occupied by a chloride ion, and nitrate and chloride ions are disordered in the channel site at 2/3, 1/3, z. A lattice water molecule is also present in the channels parallel to c that host nitrate and chloride. The empirical formula Cu36Cl8.13(NO3)1.09(OH)62.78Ã"šÃ‚·5.22H2O was obtained on the basis of the refinement of the structure (R1=0.042). Site occupancies associated with the complex pattern of solid solution phenomena and thus the stoichiometry are remarkably similar to those found in the structure of a sample of buttgenbachite from the Cole shaft, Bisbee, Arizona.