Clays and Clay Minerals, Vol. 58, No. 4, 522–531, 2010.
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Authors
Kogure, Toshihiro
Drits, Victor A.
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Celadonite , Cis-vacant , Illite , TEM , Trans-vacant
Alternative Title
Structural Change In Celadonite And Cis-vacant Illite By Electron Radiation In TEM
Abstract
High-resolution transmission electron microscopy (HRTEM) images oftwo 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 highresolution transmission electron microscopy (HRTEM) images indicates a different cation distribution in the sheet. Furthermore, the b angle for the 1M polytype derived from the HRTEM images is ~98.5º, which is considerably smaller than that (~100.5º) reported for celadonite. In previous works, cation migration from the tv to cv-like configurations and a decrease in the b 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 ofHRTEM images from 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 b angle (~102.5º) from that in the natural state (101.5º) estimated from the HRTEM images also supports this interpretation. This phenomenon is a large obstacle to the investigation ofphyl losilicates containing Al-rich cv and Mg,Fe-rich tv 2:1 layers, using HRTEM.
Description
gsccm58407-kogrev1.pdf -- 1,181KB
Citation
Clays and Clay Minerals, Vol. 58, No. 4, 522–531, 2010.
Publisher
The Clay Minerals Society
License
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