• 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 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) ų. 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.