• journal_title：Clays and Clay Minerals
• Contributor：Toshihiro Kogure ; Jessica Elzea-Kogel ; Cliff T. Johnston ; David L. Bish
• Publisher：Clay Minerals Society
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.1346/CCMN.2010.0580106
• journal_abbrev：Clays and Clay Minerals
• issn：0009-8604
• volume：58
• issue：1
• firstpage：62
• section：Articles

Although structural disorder in kaolinite has been investigated extensively, it is still not understood properly. To investigate the problem, a kaolinite specimen of sedimentary origin from Capim, Brazil, was examined, mainly by transmission electron microscopy (TEM). Selected-area electron diffraction (SAED) along the X_i ([100], [110], and [11̅0]) directions shows various features, from completely discrete patterns to heavily streaked ones along the c* direction, suggesting that the degree of stacking disorder is variable among individual grains. High-resolution TEM images indicate that stacking faults are mainly caused by disorder of alternating t₁ (~−a/3) and t₂ (−a/3 +b/3) layer displacements. Furthermore, stacking faults have been observed (1) as isolated stacking faults (e.g. insertion of an isolated t₂ ‘fault’ in an ordered sequence with t₁ layer displacement) and (2) as interstratification of two kinds of multilayer blocks having regular t₁ and t₂ layer displacements. A mixture of grains with various degrees and modes of disorder with alternating t₁ and t₂ layer displacements may explain the experimental profile of the 02, 11 X-ray diffraction band.

Faults related to displacement of the octahedral vacancy and/or to layer rotation were also observed in HRTEM images. The SAED patterns along the Y_i ([010], [310], and [31̅0]) directions occasionally have extra spots and/or streaks, suggesting the presence of stacking sequences with (±60°, 180°) mutual layer rotation and/or with (0, ±b/3) layer displacements. The local dickite or nacrite-like fragments formed by these faults are in qualitative agreement with recent low-temperature FTIR results from this sample, where distinct ν(OH) absorption bands reflect multiple interlayer O–H…O environments that are possibly ascribed to dickite and nacrite.