A new mineral, zincolibethenite, CuZnPO_4OH, a stoichiometric species of specific site occupancy

摘要

Tiny green crystals from Kabwe, Zambia, associated with hopeite and tarbuttite (and probably first recorded in 1908 but never adequately characterized because of their scarcity) have been studied by X-ray diffraction, microchemical and electron probe microanalysis, infrared spectroscopy, and synthesis experiments. They are shown to be oithorhombic, stoichiometric CuZnPO_4OH, of species rank, forming the end-member of a solid-solution series to libethenite, Cu_2PO_4OH, and are named zincolibethenite. The libethenite structure is unwilling to accommodate any more Zn substituting for Cu at atmospheric pressure, syntheses using Zn-rich solutions precipitating a mixture of zincolibethenite with hopeite, Zn_3(PO_4)_2 center dot 4H_2O. Single-crystal X-ray data confirm that the Cu(II) occupies the Jahn-Teller distorted 6-coordinate cation site in the libethenite lattice, and the Zn(II) occupies the 5-coordinate site. The space group of zincolibethenite is Pimm, the same as that of libethenite, with unit-cell parameters a = 8.326, b = 8.260, c = 5.877 A, V= 404.5 A~3, Z = 4, calculated density = 3.972 g/cm~3 (libethenite has a = 8.076, b = 8.407, c = 5.898 A, V = 400.44 A~3, Z = 4, calculated density = 3.965 g/cm~3). Zincolibethenite is biaxial negative, with 2V_(alpha)(calc.) of 49 deg, r