Parallel intergrowths in cronstedtite-1T; implications for structure refinement

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doi: 10.1346/CCMN.2004.0520507
Authors:Durovic, Slavomil; Hybler, Jiri; Kogure, Toshihiro
Author Affiliations:Primary:
Slovak Academy of Sciences, Institute of Inorganic Chemistry, Bratislava, Slovakia
Other:
Science Academy of Czech Republic, Czech Republic
University of Tokyo, Japan
Volume Title:Clays and Clay Minerals
Source:Clays and Clay Minerals, 52(5), p.613-621. Publisher: Clay Minerals Society, Clarkson, NY, United States. ISSN: 0009-8604
Publication Date:2004
Note:In English. 20 refs.; illus.
Summary:Cronstedtite is a member of the kaolin-serpentine group. It yields a wealth of more or less disordered polytypes. The crystals of polytype 1T (space group P31m, a = 5.512, c = 7.106 Å) contain, within coherently scattering blocks, variable concentrations of stacking faults so that domains of the basic 3D periodic structure can be shifted by 1/3(a2-a1) or 1/3 (a1-a2). These so-called OD parallel intergrowths have been confirmed by high-resolution transmission electron microscopy. The effect manifests itself in the diffraction pattern so that reflections with h-k = 3n--the family reflections--are always sharp, whereas remaining reflections--the characteristic polytype reflections--may be smeared out parallel to c*. The intensities of the latter are thus underestimated during diffractometer measurements. An analysis of such multiple OD intergrowths reveals that the moduli of structure factors for all characteristic (i.e. non-family) polytype reflections are reduced relative to those calculated for the non-intergrown basic structure, by a common factor. This fact usually leads to the appearance of ghost peaks in Fourier maps and to their erroneous interpretation. The structure of the basic model can, however, be refined much better if two scale factors are assigned to the family and non-family reflections, respectively.
Sections:Clay minerals
Subsections:Techniques; structure; properties
Subjects:Clay minerals; Cronstedtite; Crystal structure; Data processing; Equations; Fourier analysis; Intergrowths; Kaolinite; Order-disorder; Polytypism; Rietveld refinement; Serpentine group; Sheet silicates; Silicates; Space groups; TEM data; X-ray diffraction data; Cornwall England; England; Europe; Great Britain; Herja; Maramures Romania; Romania; Southern Europe; Transylvania; United Kingdom; Western Europe
Abstract Numbers:04M/4575
Record ID:2005004564
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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