Crystal Structure of Complex Natural Aluminum Magnesium Calcium Iron Oxideстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The structure of a new natural oxide found near the Tashelga River (Eastern Siberia) was studied by X-ray diffraction. The pseudo-orthorhombic unit cell parameters are a = 5.6973(1) angstrom, b = 17.1823(4) angstrom, c = 23.5718(5) angstrom, beta = 90 degrees, sp. gr. Pc. The structure was refined to R = 0.0516 based on 4773 reflections with vertical bar F vertical bar > 7 sigma(F) taking into account the twin plane perpendicular to the z axis (the twin components are 0.47 and 0.53). The crystal-chemical formula (Z = 4) is Ca(2)Mg(2)(IV)Fe(2)((2+)IV)[Al(14)(VI)O(31)(OH)][Al(2)(IV)O][Al(IV)][Al( IV)(OH)], where the Roman numerals designate the coordination of the atoms. The structure of the mineral is based on wide ribbons of edge-sharing Al octahedra (an integral part of the spinel layer). The ribbons run along the shortest x axis and are inclined to the y and z axes. The adjacent ribbons are shifted with respect to each other along the y axis, resulting in the formation of step-like layers in which the two-ribbon thickness alternates with the three-ribbon thickness. Additional Al octahedra and Mg and Fe(2+) tetrahedra are located between the ribbons. The layers are linked together to form a three-dimensional framework by Al tetrahedra, Ca polyhedra, and hydrogen bonds with the participation of OH groups.