- © 2013 Mineralogical Society of America
The crystal structure of vladkrivovichevite, a new complex lead oxychloride mineral from the Kombat Mine, Grootfontein, Namibia, has been solved by direct methods and refined to R1 = 0.048 for 3801 unique observed reflections. The mineral is orthorhombic, Pmmn, a = 12.759(1), b = 27.169(4), c = 11.515(1) Å, and V = 3992.0(9) Å3. The structure of vladkrivovichevite belongs to a novel type of layered Pb oxychloride structure. The structure contains 12 symmetrically independent Pb sites. All Pb sites have strongly asymmetric coordination. Two B atoms form slightly distorted BO3 triangles. One symmetrically independent Mn atom forms five Mn-O bonds and one Mn-Cl bond by forming MnO5Cl octahedra. The O1, O2, O10, O11, and O12 atoms are tetrahedrally coordinated by four Pb atoms each, forming OPb4 oxocentered tetrahedra. The O7 site has a remarkable octahedral coordination, consisting of four Pb and two Mn atoms. The O1Pb4, O2Pb4, O10Pb4, and O11Pb4 tetrahedra share common edges to produce bands interconnected by O12Pb4 tetrahedra, forming a [O18Pb32]28+ layer. A O7Pb4Mn2 heterometallic oxocentered octahedron serves as the core of the [OPb4Mn2Cl2(BO3)8]16− clusters that link to the [O18Pb32]28+ layer via BO3 triangles. The presence of [OPb4Mn2Cl2(BO3)8]16− clusters is associated with large cross-like vacancies in the [O18Pb32]28+ layer.