A transmission electron microscopy (TEM) investigation was undertaken in order to elucidate the nature of the structural disorder in a tobelite specimen from the sedimentary rocks of the Armorican sandstones (western France). This structural disorder may be the origin of residual electron-density maxima in difference-Fourier maps reported previously in single-crystal XRD studies of tobelite. The TEM investigation of tobelite confirmed that it is the 2M2 polytype in subfamily-B, but the ordered sequence is interrupted by numerous stacking faults parallel to (001), for which the stacking vectors belong to both subfamilies-A and -B of mica polytypes, with a prevalence of the latter. Chemical heterogeneity depending on the Si/Al ratio and Na and Mg concentration was observed at the nanoscale among different mica lamellae in a single crystal. The observed variations are consistent with a change in mica chemistry leading to interlayer vacancies which may cause shortening of the interlayer separation, as revealed by the single-crystal structure refinements.

Capitani, G., Schingaro, ., E, L., M, M., E, S. (2016). Structural anomalies in tobelite-2M2 explained by high resolution and analytical electron microscopy. MINERALOGICAL MAGAZINE, 80(1), 143-156 [10.1180/minmag.2015.079.7.14].

Structural anomalies in tobelite-2M2 explained by high resolution and analytical electron microscopy

CAPITANI, GIANCARLO;
2016

Abstract

A transmission electron microscopy (TEM) investigation was undertaken in order to elucidate the nature of the structural disorder in a tobelite specimen from the sedimentary rocks of the Armorican sandstones (western France). This structural disorder may be the origin of residual electron-density maxima in difference-Fourier maps reported previously in single-crystal XRD studies of tobelite. The TEM investigation of tobelite confirmed that it is the 2M2 polytype in subfamily-B, but the ordered sequence is interrupted by numerous stacking faults parallel to (001), for which the stacking vectors belong to both subfamilies-A and -B of mica polytypes, with a prevalence of the latter. Chemical heterogeneity depending on the Si/Al ratio and Na and Mg concentration was observed at the nanoscale among different mica lamellae in a single crystal. The observed variations are consistent with a change in mica chemistry leading to interlayer vacancies which may cause shortening of the interlayer separation, as revealed by the single-crystal structure refinements.
Articolo in rivista - Articolo scientifico
2M2 polytype; electron microscopy; stacking disorder; tobelite;
2M2 polytype; electron microscopy; stacking disorder; tobelite
English
143
156
14
Capitani, G., Schingaro, ., E, L., M, M., E, S. (2016). Structural anomalies in tobelite-2M2 explained by high resolution and analytical electron microscopy. MINERALOGICAL MAGAZINE, 80(1), 143-156 [10.1180/minmag.2015.079.7.14].
Capitani, G; Schingaro, ; E, L; M, M; E, S
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/136435
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