Clays and Clay Minerals

, Volume 53, Issue 3, pp 201–210 | Cite as

Polytype and Morphology Analyses of Kaolin Minerals By Electron Back-Scattered Diffraction

  • Toshihiro KogureEmail author
  • Atsuyuki Inoue
  • Daniel Beaufort


The electron back-scattered diffraction (EBSD) technique has been applied to fine-grained kaolin minerals to determine the polytypes (kaolinite, dickite and nacrite) of individual grains and their crystallographic orientations in a scanning electron microscope (SEM). Because kaolin minerals are prone to radiation damage by the intense electron beam necessary to obtain EBSD patterns, the beam has to be rastered across the specimens during pattern acquisition. Kaolinite-dickite and nacrite are easily distinguished by their trigonal or hexagonal symmetry about the [001]* direction, respectively, of the Kikuchi bands with k = 3n. Dickite can be differentiated from kaolinite by mirror symmetry parallel to the ac plane, and by the characteristic contrast of HOLZ rings.

As EBSD analysis is performed using a SEM, morphological characters can be correlated with polytypes. Dickite fragments could be discerned as oriented overgrowths on nacrite plates. Dickite was observed to always adopt euhedral shapes in a diagenetic mixture of kaolinite and dickite. Lath-shaped dickite is elongated along the a axis direction. Rhombohedral dickite consists of crystals with {1̄11} indexed to the side facets.

Key Words

Dickite EBSD Kaolin Minerals Kaolinite Morphology Nacrite Polytype SEM 


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Copyright information

© The Clay Minerals Society 2005

Authors and Affiliations

  • Toshihiro Kogure
    • 1
    • 2
    Email author
  • Atsuyuki Inoue
    • 3
  • Daniel Beaufort
    • 4
  1. 1.Department of Earth and Planetary Science, Graduate School of ScienceThe University of TokyoTokyoJapan
  2. 2.Japan Science and Technology CorporationCRESTSaitamaJapan
  3. 3.Department of Earth Sciences, Faculty of ScienceChiba UniversityChibaJapan
  4. 4.HydrASA UMR 6532 CNRSUniversité de PoitiersPoitiers CedexFrance

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