Clays and Clay Minerals, Vol. 57, No. 1, 104–114, 2009.
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Authors
Emmerich, Katja
Wolters, Felicitas
Kahr, Guenter
Lagaly, Gerhard
Issue Date
2009
Type
Article
Language
Keywords
Periodicals , Geology , 2:1 Layer Silicates , Cis-vacant , Classification , Dioctahedral , Layer Charge , Montmorillonite , Smectite , Trans-vacant
Alternative Title
Clay Profiling: The Classification Of Montmorillonites
Abstract
Montmorillonites, with the general composition M+ x(Si4-yAly)[(Al,Fe3+)2-z(Mg,Fe2+)z] O10(OH)2 where x = x = 0.2-0.6, x = y+z, and y<<z, vary widely in composition and structure. The commonly used classification into fivemon tmorilloniteand two beidellitegroups for thes olid-solution sequence does not allow an unambiguous classification with respect to structural features and the resulting properties. The smectite structure reveals five features that allow an unambiguous description of a sample: (1) identification as either a dioctahedral or a trioctahedral smectite; (2) layer charge; (3) charge distribution between tetrahedral and octahedral sheets; (4) cation distribution within the octahedral sheet; and (5) Fe content. In addition, the nature of interlayer cations should be given as they influence certain properties of montmorillonites. Analytical methods are now available to measure and determine these structural features. Therefore, a precise classification for montmorillonites requires determination of layer charge and exchangeable cations, analysis of chemical composition, and thermal analysis (to determine the octahedral structure), in addition to X-ray diffraction analysis. A comprehensive classification of montmorillonites based on these parameters is proposed. Ninety-six structural variations (expressed by systematic names) theoretically exist within the montmorillonite– beidellite series. Descriptive names can be used to elucidate the macroscopic properties of the montmorillonite samples in question.
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gsccm57110-emm.pdf -159KB
Citation
Clays and Clay Minerals, Vol. 57, No. 1, 104–114, 2009.
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