On the crystal chemistry of the wardite, NaAl3(PO4)2(OH)4 x 2H2O
Wardite, ideally NaAl3(PO4)2(OH)4 x 2H2O, is a hydrothermal mineral, which occurs in phosphate-rich zones of granite pegmatites. Its crystal structure was solved and refined by Fanfani et al. (1970). To the best of our knowledge, no more recent data are available in the open literature. The structure contain a total amount of 18 wt% of H2O. The quality of the data at that time (by Wissenberg method with multiple-film integrated photographs) did not allow to locate unambiguously the H sites, leaving open questions about the configuration of the H2O molecules and OH-groups and, as a consequence, about the H-bonding scheme in wardite structure, which is completely unknown. The aim of this study is to provide a single-crystal neutron structure refinement of wardite based on modern standards and with a general improvement of the whole structure model. More specifically, we expect to provide: a) the reliable location of the proton sites and the real topological configuration of the OH-groups and H2O molecules, for a full description of the atomic relationship via the H-bonds; b) the anisotropic displacement parameters of all the atomic sites, H-sites included.
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GATTA Giacomo Diego; FABELO ROSA Oscar Ramon and FERNANDEZ DIAZ Maria Teresa. (2018). On the crystal chemistry of the wardite, NaAl3(PO4)2(OH)4 x 2H2O. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.5-11-430
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