Structural change in celadonite and cis-vacant illite by electron radiation in TEM
Kogure, Toshihiro (The University of Tokyo. Department of Earth and Planetary Science. Graduate School of Science)
Drits, Victor A. (Geological Institute of the Russian Academy of Sciences)

Data:	2010
Resum:	High-resolution transmission electron microscopy (HRTEM) images of two dioctahedral micas, celadonite and cis-vacant (cv) illite, were examined in detail to understand the effects of electron radiation on their structures during image acquisition. Celadonite, a dioctahedral mica with Fe and Mg as major octahedral cations, originally has a trans-vacant (tv) octahedral sheet but the contrast in the high- resolution transmission electron microscopy (HRTEM) images indicates a different cation distribution in the sheet. Furthermore, the β angle for the 1M polytype derived from the HRTEM images is ~98. 5°, which is considerably smaller than that (~100. 5°) reported for celadonite. In previous works, cation migration from the tv to cv-like configurations and a decrease in the β angle after dehydroxylation of celadonite/ glauconite by heating were reported. The same phenomenon, dehydroxylation and subsequent cation migration, probably occurs by electron radiation in TEM. However, the new cation-distribution models derived from HRTEM images along the [100] and [110] directions are not in agreement. On the other hand, the contrast in a number of HRTEM images rom an illite specimen in which cv-illite is dominant is the same as that for the tv-dioctahedral layer. This result is also interpreted as cation migration accompanied by dehydroxylation in TEM, as reported in heated cv-illite. The increased β angle (~102. 5°) from that in the natural state (101. 5°) estimated from the HRTEM images also supports this interpretation. This phenomenon is a large obstacle to the investigation ofphyllosilicates containing Al-rich cv and Mg,Fe-rich tv 2:1 layers, using HRTEM.
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Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Celadonite ; Cis-vacant ; Illite ; TEM ; Trans-vacant
Publicat a:	Clays and Clay Minerals, Vol. 58, Núm. 4 (2010) , p. 522-531, ISSN 1552-8367

DOI: 10.1346/CCMN.2010.0580407

10 p, 1.8 MB  Accés restringit a la UAB

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