Refinement of the kaolinite structure from single-crystal synchrotron data

The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRF Grenoble, France (lambda = 0.6883, T = room temperature). The volume of the crystals was 8 and 0.8 mu m(3), respectively. Unit-cell parameters are: a = 5.154(9) Angstrom, b = 8.942(4) Angstrom, c = 7.401(10) Angstrom, alpha = 91.69(9)degrees, beta = 104.61(5)degrees, gamma = 89.82(4)degrees. Space group Cl is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined also. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk not equal 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.