Single crystal refinement of the structure of baghdadite from Fuka (Okayama Prefecture, Japan)

The crystal structure of baghdadite, ideally Ca(3)Zr(Si(2)O(7))O(2), was refined using 1986 reflections to R = 0.034. Baghdadite is monoclinic, space group P2(1)/a, with cell parameters a 10.432(3), b 10.163(2), c 7.356(2) angstrom, beta 90.96(2)degrees. The refined crystal structure is in agreement with the structure of synthetic Ca(3)ZrSi(2)O(9). The structure is characterized by the presence of walls of cation polyhedra, four columns large, linked together by both direct connection as well as by disilicate groups. Baghdadite is the first phase in the cuspidine group in which the Pauling's fourth rule is violated.