The crystal structure of jennite, Ca9Si6O18(OH)6•8H2O

The crystal structure of jennite is solved and refined in the space group P (1) over bar by using single crystal X-ray diffraction data collected at the Elettra synchrotron radiation facility on a very thin crystal from Fuka, Japan. The triclinic refined unit cell is a = 10.576(2) Angstrom, b = 7.265(2) Angstrom, c = 10.931(3) Angstrom, alpha = 101.30(1), beta = 96.98(1), gamma = 109.65(1)degrees. The structure of jennite is built up by three distinct modules: ribbons of edge-sharing calcium octahedra, silicate chains of wollastonite-type running along b, and additional calcium octahedra on inversion centres. The structural results indicate that the crystal chemical formula of jennite is Ca9Si6O18(OH)(6)(.)8H(2)O, and that all the hydroxyl groups are bonded to three calcium cations; SiOH groups are not found. The structural disorder observed in jennite is explained on the basis of the OD theory, and a model for the structure of metajennite, the dehydration product of jennite, is proposed. (C) 2004 Elsevier Ltd. All rights reserved.