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Ordering of cations in the voids of the anionic framework of the crystal structure of catapleiite |
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| Authors: | O V Yakubovich O V Karimova A G Ivanova V O Yapaskurt N V Chukanov P M Kartashov |
| Institution: | 17764. Faculty of Geology, Moscow State University, Moscow, 119992, Russia 27764. Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia 37764. Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333, Russia 47764. Institute of the Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Noginskii raion, Moscow oblast, 142432, Russia |
| Abstract: | The pseudohexagonal crystal structure of the mineral catapleiite Na1.5Ca0.2ZrSi3(O,OH)9] · 2(H2O,F) from the Zhil’naya Valley in the central part of the Khibiny alkaline massif (Kola Peninsula, Russia) is studied by X-ray diffraction (XCalibur-S diffractometer, R = 0.0346): a = 20.100(4), b = 25.673(5), and c = 14.822(3) Å; space group Fdd2, Z = 32, and ρcalcd = 2.76 g/cm3. Fluorine atoms substituting part of H2O molecules in open channels of the crystal structure have been found for the first time in the catapleiite composition by microprobe analysis. The pattern of distribution of Na and Ca atoms over the voids of the mixed anionic framework consisting of Zr-octahedra and three-membered rings of Si-tetrahedra accounts for the pronounced pseudoperiodicity along the a and c axes of the pseudohexagonal unit cell and for the lowering of crystal symmetry to the orthorhombic one. It is shown that part of the hydrogen atoms of water molecules is statistically disordered; their distribution correlates with the pattern of the population of large eight-vertex polyhedra by Na and Ca atoms. |
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