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Morphology of Clay Minerals in the Smectite-to-Illite Conversion Series by Scanning Electron Microscopy

Published online by Cambridge University Press:  02 April 2024

W. D. Keller ,
R. C. Reynolds  and
Atsuyuki Inoue
W. D. Keller
Affiliation:
Department of Geology, University of Missouri-Columbia, Columbia, Missouri 65211
R. C. Reynolds
Affiliation:
Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755
Atsuyuki Inoue
Affiliation:
Geological Institute, College of Arts and Sciences, Chiba University, Chiba 260, Japan
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Abstract

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The morphology of illite/smectite (I/S) from deeply buried bentonites and hydrothermally altered Tertiary volcanic rocks from Japan changes in parallel with the proportion of expandable layers in the I/S. As viewed by scanning electron microscopy, the morphologies range from the typical “cornflake,” “maple leaf,” or “honeycomb” habit of smectite to the typical platy or scalloped (with curled points) habit of illite. Although the changes are more subtle near either end member, at a composition of 60-70% illite layers, the morphology changes from sponge-like or cellular to platy or ribbon-like. The change of morphology at this composition correlates with a change in layer stacking from turbostratic to rotational ordering of the 1Md type. Turbostratic stacking can be thought of as randomly distributed translations of successive layers by any magnitude and in any direction. The rotationally ordered structure, which allows nearly precise juxtaposition of quasihexagonal oxygen surfaces from adjacent layers, probably permits more crystalline regularity in the a-b plane, which promotes a more plate-like or sheet-like habit.

Keywords

Burial diagenesisHydrothermal alterationIllite/smectiteMorphologyScanning electron microscopySmectite-to-illite conversion
Type
Research Article
Information
Clays and Clay Minerals , Volume 34 , Issue 2 , April 1986 , pp. 187 - 197
Copyright
Copyright © 1986, The Clay Minerals Society

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