Application of Rietveld Refinement Techniques to a Disordered IIb Mg-Chamosite

Jeffrey R. Walker and David L. Bish
Department of Geology and Geography, Vassar College, Poughkeepsie, New York 12601
EES-1. Mailstop D469, Los Alamos National Laboratory, Los Alamos, New Mexico 87545

Abstract: The structure of a disordered IIb Mg-chamosite was studied using Rietveld refinement techniques and powder X-ray diffraction (CuKα, 18–120° 2θ in 0.02° 2θ increments). The refinement in space group Cl-̄ yielded high precision lattice parameters (a = 5.36982(5)Å, b = 9.3031(9)Å, c = 14.2610(6)Å, α = 90.315(5)°, β = 97.234(7)°, γ = 90.022(9)°) and atomic coordinates very similar to previous studies. However, the presence of semi-random stacking in this specimen created a situation in which not all atoms could be precisely located: the positions of the octahedral cations and anions which repeat at intervals of ±b/3 could be uniquely determined in three dimensions whereas only the z parameter of the other atoms could be refined. The reasonable appearance of the final model, despite the fact that many of the atom positions could be located in only one dimension, may have resulted because all of the atoms in this structure except O(5) repeat at intervals which are very nearly ±b/3.

Key Words: Chlorite • Disorder • Rietveld refinement

Clays and Clay Minerals; June 1992 v. 40; no. 3; p. 319-322; DOI: 10.1346/CCMN.1992.0400311
© 1992, The Clay Minerals Society
Clay Minerals Society (www.clays.org)