Synchrotron x-ray Rietveld study of perlialite, the natural counterpart of synthetic zeolite-L

The crystal structure of perlialite from the Murun Massif, U.S.S.R. was determined and refined using synchrotron X-ray powder data. The framework type of this natural zeolite is the same as synthetic zeolite Linde-L. Extraframework cation and water oxygen position were located, and the locations and occupancies show large differences with respect to the cation and water sites previously reported for the synthetic zeolites K-L and Ba, K-L. Refinement results and subsequent chemical analysis on the Murun sample lead us to revise the unit cell formula of perlialite to: K8Tl4Al12Si24O72 . 20H2O. The chemical formula has a Tl content not shown in the original chemical analyses of the species. Space group P 6/m mm was confirmed and the refined cell parameters are a = 18.5432(4), c = 7.5310(3) angstrom. A Rietveld refinement of the same sample using conventional automated powder diffractometer data confirmed the structural model and crystallochemical details.