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POLYMORPH AND POLYTYPE IDENTIFICATION FROM INDIVIDUAL MICA PARTICLES USING SELECTED AREA ELECTRON DIFFRACTION

Abstract : Dioctahedral micas are composed of two tetrahedral sheets and one octahedral sheet to form TOT or 2:1 layers. These minerals are widespread and occur with structures differing by (i) the layer stacking mode (polytypes), (ii) the location of vacancies among non-equivalent octahedral sites (polymorphs), and (iii) the charge-compensating interlayer cation and isomorphic substitutions. The potential of parallel-illumination electron diffraction (ED) is assessed here to determine the polytype/polymorph of individual crystals of finely divided dioctahedral micas and to image their morphology. ED patterns are calculated along several zone axes close to the c *-and c-axes using the kinematical approximation for trans-and cis-vacant varieties of the four common mica polytypes (1 M , 2 M 1 , 2 M 2 , and 3 T). When properly oriented, all ED patterns have similar geometry, but differ by their intensity distribution over hk reflections of the zero-order Laue zone. Differences are enhanced for ED patterns calculated along the [001] zone-axis. Identification criteria are proposed for polytype/polymorph identification, based on the qualitative distribution of bright and weak reflections. A database of ED patterns calculated along other zone-axes is provided in case the optimum [001] orientation cannot be found. Different polytype/polymorphs may exhibit similar ED patterns depending on the zone axis considered.
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Submitted on : Tuesday, November 24, 2020 - 8:23:06 PM
Last modification on : Thursday, November 26, 2020 - 3:28:56 AM

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Anne-Claire Gaillot, Victor Drits, Bruno Lanson. POLYMORPH AND POLYTYPE IDENTIFICATION FROM INDIVIDUAL MICA PARTICLES USING SELECTED AREA ELECTRON DIFFRACTION. Clays and Clay Minerals, Clay Minerals Society, 2020, 68 (4), pp.334-346. ⟨10.1007/s42860-020-00075-9⟩. ⟨insu-02984565⟩

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