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

The crystal structure of jennite is solved and refined in the space group P1?, 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) Å, b=7.265(2) Å, c=10.931(3) Å, α=101.30(1), β=96.98(1), γ=109.65(1)°. 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)₆·8H₂O, 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.