Refinement of the Kaolinite Structure from Single-Crystal Synchrotron Data

R. B. Neder1, †, M. Burghammer1, ‡, TH. Grasl1, H. Schulz1, A. Bram2, § and S. Fiedler2
1 Institut für Kristallographie, Theresienstr. 41, 80333 München, Germany
2 ESRF, B.P. Box 220, 38043 Grenoble, France
Present address: Mineralogisches Institut, Am Hubland, 97074 Würzburg, Germany.
Present address: ESRF B.P. Box 220, 38043 Grenoble, France.
§ Present address: Siemens AG.

Abstract: The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRE Grenoble, France (λ = 0.6883, T = room temperature). The volume of the crystals was 8 and 0.8 µm3, respectively. Unit-cell parameters are: a = 5.154(9) Å, b = 8.942(4) Å, c = 7.401(10) Å, α = 91.69(9)°, β = 104.61(5)°, γ = 89.82(4)°. Space group C1 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 ≠ 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.

Key Words: Crystal Structure • Diffuse Scattering • H-Positions • Kaolinite • Microcrystal • Single Crystal Refinement • Synchrotron Radiation

Clays and Clay Minerals; August 1999 v. 47; no. 4; p. 487-494; DOI: 10.1346/CCMN.1999.0470411
© 1999, The Clay Minerals Society
Clay Minerals Society (www.clays.org)