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CBED and ALCHEMI investigation of local symmetry and Al, Si ordering in K-feldspars

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Abstract

CBED (convergent beam electron diffraction) and ALCHEMI (atom location by channelling enhanced microanalysis) have been used to determine the symmetry and Al-order parameter 2t 1 within homogeneous regions (of the order of 100 nm in diameter) of high sanidine and low microcline. The results are in excellent agreement with those obtained on the same crystals from X-ray measurements of average T-O bond lengths. In view of this agreement, CBED and ALCHEMI were then applied to an orthoclase with a well-developed tweed microstructure. The results indicate that the specimen is partially ordered and that the average symmetry is triclinic. The lattice modulations involve values of γ* in the range 90°<γ*<90.5°, with correspondingly small variations of 2t 1 about an average value of 0.67.

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Authors and Affiliations

  1. Research School of Earth Sciences, Australian National University, 2601, Canberra, ACT, Australia

    A. C. McLaren & J. D. Fitz Gerald

  2. Research School of Chemistry, Australian National University, 2601, Canberra, ACT, Australia

    A. C. McLaren

Authors
  1. A. C. McLaren
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  2. J. D. Fitz Gerald
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McLaren, A.C., Fitz Gerald, J.D. CBED and ALCHEMI investigation of local symmetry and Al, Si ordering in K-feldspars. Phys Chem Minerals 14, 281–292 (1987). https://doi.org/10.1007/BF00307995

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  • DOI: https://doi.org/10.1007/BF00307995

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