Uranotungstite is an uranyl-tungstate mineral that was until recently only partially characterized with a formula originally given as (Fe2+,Ba,Pb)(UO2)2(WO4)(OH)4·12H2O and an unknown crystal structure. This mineral has been reinvestigated by electron microprobe analysis coupled with three-dimensional electron diffraction. According to the electron microprobe data, the holotype material from the Menzenschwand uranium deposit (Black Forest, Germany) has the empirical formula (Ba0.35Pb0.27)Σ0.62[(U6+O2)2(⁠W0.986+☐0.75)O4.7(OH)2.5(H2O)1.75](H2O)1.67 (average of 8 points calculated on the basis of 2U apfu; H2O content derived from the structure). According to the precession-assisted 3D ED data, holotype uranotungstite from Menzenschwand is monoclinic, P21/m, with a = 6.318(5) Å, b = 7.388(9) Å, c = 13.71(4) Å, β = 99.04(13)°, and V = 632(2) Å3 (Z = 2). The structure refinement of the 3D ED data using the dynamical approach (Robs = 0.0846 for 3287 independent observed reflections) provided a structure model composed of heteropolyhedral sheets. A β-U3O8-type sheet of idealized composition [(UO2)2W6+Fe0.253+☐0.75O4.75(OH)1.5(H2O)1.75]0.25– is composed of UO7 polyhedra linked by (W,Fe)O5 polyhedra in which the W:Fe ratio is variable as well as the bulk occupancy of this site; the W site may also host a minor proportion of Cu, Mg, or V. In uranotungstite, the interlayer spaces between adjacent U-W-O sheets host water on one side and, on the other side, a partially occupied cation site mostly occupied by Ba and, to a lesser extent, Pb, as well as a partially occupied H2O site. This work is the first structural description of a natural uranyl-tungstate mineral and confirms the great structural and chemical flexibility of β-U3O8 type of sheets.

中文翻译：

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铀钨钨矿，唯一的天然铀基钨酸盐：从 3D 电子衍射揭示的晶体结构

铀钨钨矿是一种铀-钨酸盐矿物，直到最近才以最初给出的分子式 (Fe2+,Ba,Pb)(UO2)2(WO4)(OH)4·12H2O 和未知的晶体结构对其进行部分表征。这种矿物已通过电子探针分析结合三维电子衍射进行了重新研究。根据电子微探针数据，Menzenschwand 铀矿床（德国黑森林）的正型材料具有经验公式 (Ba0.35Pb0.27)Σ0.62[(U6+O2)2(⁠W0.986+☐0.75 )O4.7(OH)2.5(H2O)1.75](H2O)1.67（以 2U apfu 计算的 8 点平均值；H2O 含量来源于结构）。根据进动辅助 3D ED 数据，来自 Menzenschwand 的正型铀钨钨矿为单斜晶系，P21/m，a = 6.318(5) Å, b = 7.388(9) Å, c = 13.71(4) Å, β = 99.04( 13)°，V = 632(2) Å3 (Z = 2)。使用动力学方法对 3D ED 数据进行结构细化（对于 3287 次独立观察到的反射，Robs = 0.0846）提供了由异多面体片组成的结构模型。理想化组成[(UO2)2W6+Fe0.253+☐0.75O4.75(OH)1.5(H2O)1.75]0.25-的β-U3O8型片材由(W,Fe)O5多面体连接的UO7多面体组成其中 W:Fe 比率是可变的以及该站点的大量占用；W 位点也可能含有少量的 Cu、Mg 或 V。在铀钨钨矿中，相邻 UWO 片之间的层间空间在一侧有水，而在另一侧，部分占据的阳离子位点主要由 Ba 占据，并且，在较小程度上，Pb，以及部分占用的 H2O 站点。