ON ZEOPHYLLITE FROM RADEJCIN, CESKE STREDOHORI MTS - X-RAY AND IR-INVESTIGATIONS

A redetermination of the crystal structure of zeophyllite, idealized C a13Si10O28F10.6H(20) [a=9.377(2), c=36.57(2) Angstrom; Z=3], space gro up R (3) over bar (No. 148) yielded R = 0.033 for 2238 observed single crystal X-ray data (Fo > 3 sigma(F0),). The atomic coordinates in com bination with the anisotropic thermal displacement parameters as well as the internal R-value from merging equivalent intensities gave no ev idence for a violation of trigonal symmetry. The structure is characte rized by SiO4 tetrahedra combined to open branched vierer single layer s in an arrangement normal to the threefold axes. These layers are con nected via the Ca(O,F)(x), polyhedra and hydrogen bridges to a framewo rk with a pronounced cleavage parallel to (00.1). The statistic occurr ence of Si-OH groups in parts of the structure was confirmed by IR-inv estigations.