Zeolites of the phillipsite family. Refinement of the crystal structures of phillipsite and harmotome
Acta Crystallographica Section B
Phillipsite (K~2Ca~t.sNa~0.4Al~sSi~a0032.12H20) and harmotome (Ba~2Ca~0.sAl~sSi~11032.12H20) were found to be isostructural with the same cationic sites and water-molecule distribution within an almost identical framework. Both minerals crystallize in the monoclinic system (P21 or P2Jm) with respective cell dimensions: a= 9"865 (2), b = 14"300 (4), c= 8"668 (2)/~,//= 124"20 (3) °, and a = 9-879 (2), b= 14-139 (2), c=8.693 (2) A, fl= 124.81 (1) °. Intensity data from a 4-circle diffractometer
... e diffractometer were refined by least-squares and Fourier techniques to respective R's of 0-063 and 0.047. The aluminosilicate framework is topologically identical to that found by earlier workers. No evidence for Si,Al ordering was found. All cations and water molecules were unequivocally located although some water molecules showed large atomic displacements. There are two cation sites: one, fully occupied by K in phillipsite and Ba in harmotome, is surrounded by eight framework oxygens and four water molecules. The other site is partially occupied by Ca and Na in a distorted octahedral coordination with two framework oxygens and four water molecules. Two of the water molecules associated with Ca showed large atomic displacements consistent with partial occupancy of the Ca site. Refinement of harmotome in P21 was unsuccessful and the structure is best described in P2x/m.