Crystal structure of celadonite from the electron diffraction data

The crystal structure of the dioctahedral celadonite mica 1M (space group C2/m; R, 2.98%; 184 unique reflections) is refined from the oblique-texture electron diffraction patterns obtained with the use of imaging plates. The maximum characterizing the location and potential of the hydrogen atom of the hydroxyl group oriented into the unoccupied trans octahedron at an angle of 4.4 degrees with respect to the ab plane is revealed from the difference Fourier-potential syntheses. The O-H interatomic distance is equal to 0.98 angstrom. The superstructure reflections observed in the selected-area electron diffraction patterns for a number of particles arise from the superposition of two cells, namely, the main cell with a broken base-centered symmetry and the base-centered supercell with the triple parameter a. These reflections are caused by the ordered distribution of the trivalent and divalent cations Fe and Mg over the octahedral cis positions. (C) 2005 Pleiades Publishing, Inc.