Abstract
Crystal data and results of structure refinement using powder X-ray diffraction and Rietveld analysis for armstrongite, CaZr[Si6O15]·3H2O, are reported. Experimental data were collected using MoKα1 radiation over the range 2° - 51.98° 2θ. Armstrongite is monoclinic (space group C2, Z = 4), with a = 14.018(1) Å, b = 14.133(1) Å, c = 7.840(1) Å, β = 109.40(1)°. The crystal structure, reported by Kashaev and Sapozhnikov (1978) has been refined by Rietveld analysis, resulting in Rwp = 2.75. The structure is based on a heterogeneous octahedra-tetrahedra framework (ZrSi6O15) built by corrugated silicate sheets connected by ZrO6 octahedra. The seven-fold Ca polyhedron contains 2 H2O molecules. Two new sites for H2O molecules on the 2-fold axis in the voids of the zeolite like framework allowed to achieve the complete correspondence between chemical and structural data.
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More From: Zeitschrift für Kristallographie - Crystalline Materials
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