- journal_title：American Mineralogist
- Contributor：Oleg I. Siidra ; Sergey V. Krivovichev ; Rick W. Turner ; Mike S. Rumsey ; John Spratt
- Publisher：Mineralogical Society of America
- Date：2013-01-01
- Format：text/html
- Language：en
- Identifier：10.2138/am.2013.4244
- journal_abbrev：American Mineralogist
- issn：0003-004X
- volume：98
- issue：1
- firstpage：256
- section：Articles
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 R<sub>1sub> = 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) Å<sup>3sup>. 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 BO<sub>3sub> triangles. One symmetrically independent Mn atom forms five Mn-O bonds and one Mn-Cl bond by forming MnO<sub>5sub>Cl octahedra. The O1, O2, O10, O11, and O12 atoms are tetrahedrally coordinated by four Pb atoms each, forming OPb<sub>4sub> oxocentered tetrahedra. The O7 site has a remarkable octahedral coordination, consisting of four Pb and two Mn atoms. The O1Pb<sub>4sub>, O2Pb<sub>4sub>, O10Pb<sub>4sub>, and O11Pb<sub>4sub> tetrahedra share common edges to produce bands interconnected by O12Pb<sub>4sub> tetrahedra, forming a [O<sub>18sub>Pb<sub>32sub>]<sup>28+sup> layer. A O7Pb<sub>4sub>Mn<sub>2sub> heterometallic oxocentered octahedron serves as the core of the [OPb<sub>4sub>Mn<sub>2sub>Cl<sub>2sub>(BO<sub>3sub>)<sub>8sub>]<sup>16−sup> clusters that link to the [O<sub>18sub>Pb<sub>32sub>]<sup>28+sup> layer via BO<sub>3sub> triangles. The presence of [OPb<sub>4sub>Mn<sub>2sub>Cl<sub>2sub>(BO<sub>3sub>)<sub>8sub>]<sup>16−sup> clusters is associated with large cross-like vacancies in the [O<sub>18sub>Pb<sub>32sub>]<sup>28+sup> layer.