New Data on the Isomorphism in Eudialyte-Group Minerals. V: Crystal Structure of an Intermediate Member of the Manganoeudialyte-Ilyukhinite Isomorphous Seriesстатья
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Аннотация:The crystal structure of a high-symmetry representative of the eudialyte group from the Norra Karr massif (Sweden) has been investigated by X-ray diffraction analysis and IR spectroscopy. The trigonal unit-cell parameters are found to be a = 14.1767(4) angstrom, c = 30.286(1) angstrom, and V = 5271.3 (3) angstrom(3); sp. gr. R3m. The crystal structure is refined to the final reliability factor R = 6.4% in the anisotropic approximation of atomic displacements using 1071 reflections with F > 3 sigma(F). The idealized formula of the mineral (Z = 3) is [(Na,H3O)(13.5)REE1.5]Ca6Mn2Zr3[Si25.5O73.5]Cl center dot H2O. The problems of hydrolysis and central symmetry of minerals with eudialyte-type structure are discussed.