Skip to main content Accessibility help

Composition variation of illite-vermiculitesmectite mixed-layer minerals in a bentonite bed from Charente (France)

  • A. Meunier (a1), B. Lanson (a2) and B. Velde (a3)


Mineralogical and chemical variations were studied in the upper half of a 1 m thick discontinuous bentonite bed interlaminated in the Lower Cenomanian sedimentary formations of the northern Aquitaine basin (France). X-ray diffraction patterns obtained from the <2 mm fraction in the Ca and K-saturated states were decomposed and compared to those calculated from decomposition parameters. They revealed the presence of two highly expandable illite-expandable (I-Exp) mixedlayer minerals (MLMs). The relative proportions of the two MLMs evolve steadily with depth leading to the decrease of the cation exchange capacity and of the (Na + Ca) content towards the centre of the bentonite bed. However, the system is essentially isochemical and Mg, Al, Si, K and Fe are roughly constant in the bulk samples. It is thought that the mineralogical zonation results from the initial stages of the smectite formation in an ash layer.

In the Ca-saturated state, the expandable component of these MLMs was for the most part homogeneous with the presence of 2 sheets of ethylene glycol molecules in the interlayer. However, the heterogeneous hydration behaviour of these expandable layers was enhanced by the K-saturation test. From this test, the presence of three layer types with contrasting layer charge was evidenced from their contrasting swelling abilities. The C12-alkylammonium saturation test applied to samples in which the octahedral charge had previously been neutralized (Hofmann-Klemen treatment) showed that the tetrahedral charge is located on specific layers. These layers are responsible for the heterogeneous hydration behaviour. Low-charge smectite layers are mostly octahedrally substituted, whereas for intermediate- and high-charge layers this montmorillonitic charge is complemented by additional tetrahedral substitutions (0.30 and 0.35–0.40 charge per O10(OH)2, respectively).


Corresponding author


Hide All
Altaner, S.P. (1985) Potassium metasomatism and diffusion in Cretaceous K-bentonites from the Disturbed Belt, north-western Montana and in the Middle Devonian Tioga K-bentonite, eastern USA. PhD thesis, University of Illinois.
Altaner, S.P., Hower, J., Whitney, G. & Aronson, J.L. (1984) Model for K-bentonite formation: Evidence from zoned K-bentonites in the disturbed belt, Montana. Geology, 12, 412–415.
Calarge, L., Lanson, B., Meunier, A. & Formoso, M.L. (2003) The smectitic minerals in a bentonite deposit from Melo (Uruguay). Clay Minerals, 38, 25–34.
Cetin, K. & Huff, W.D. (1995) Layer charge of the expandable component of illite/smectite in K-bentonite as determined by alkylammonium ion exchange. Clays and Clay Minerals, 43, 150–158.
Cuadros, J. & Altaner, S.P. (1998) Compositional and structural features of the octahedral sheet in mixedlayer illite/smectite from bentonites. European Journal of Mineralogy, 10, 111–124.
Drits, V.A., Lindgreen, H., Sakharov, B.A. & Salyn, A.S. (1997) Sequence structure transformation of illitesmectite- vermiculite during diagenesis of Upper Jurassic shales, North sea. Clay Minerals, 33, 351–371.
Esposito, K.J. & Whitney, G. (1995) Thermal effects of thin igneous intrusions on diagenetic reactions in a Tertiary basin of Southwestern Washington. US Geological Survey Bulletin, 2085–C, 36 pp.
Foscolos, A.E. & Kodama, H. (1974) Diagenesis of clay minerals from lower Cretaceous shales of north eastern British Columbia. Clays and Clay Minerals, 22, 319–335.
Hoffman, J. & Hower, J. (1979) Clay mineral assemblages as low grade metamorphic geothermometers: application to the thrust faulted disturbed belt of Montana, USA. Special Publication, 26, Society of Economic Paleontologists and Mineralogists, Tulsa, Oklahoma, pp. 55–79.
Hofmann, U. & Klemen, E. (1950) Loss of exchangeability of lithium ions in bentonite on heating. Zeitschrift fur anorganische und Allgemeine Chemie, 262, 95–99.
Huff, W.D. & Türkmenoglu, A.G. (1981) Chemical characteristics of Ordovician K-bentonites along the Cincinnati Arch. Clays and Clay Minerals, 29, 113–123.
Inoue, A., Bouchet, A., Velde, B. & Meunier, A. (1989) A convenient technique to estimate smectite layer percentage in randomly interstratified illite/smectite minerals. Clays and Clay Minerals, 37, 227–234.
Lagaly, G. & Weiss, A. (1969) Determination of the layer charge in mica-type layer silicates. Proceedings of the International Clay Conference, Tokyo, 1, 61–80.
Lanson, B. (1997) Decomposition of experimental X-ray diffraction patterns (profile fitting): a convenient way to study clay minerals. Clays and Clay Minerals, 45, 132–146.
Meunier, A., Proust, D. & Moreau, P. (1999) Geological significance of two smectite-rich beds from Lower Cenomanian sediments, northern Aquitaine basin, France. Bulletin de la Société Géologique de France, 170, 873–882.
Meunier, A., Lanson, B. & Beaufort, D. (2000) Vermiculitization of smectite interfaces and illite layer growth as a possible dual model for illitesmectite illitization in diagenetic environments: a synthesis. Clay Minerals, 35, 573–586.
Moore, D.M. & Reynolds, R.C. (1989) X-ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford University Press, Oxford, UK.
Olis, A.C., Malla, P.B. & Douglas, L.A. (1990) The rapid estimation of the layer charges of 2:1 expanding clays from a single alkylammonium ion expansion. Clay Minerals, 25, 39–50.
Plançon, A. & Drits, V.A. (2000) Phase analysis of clays using an expert system and calculation programs for X-ray diffraction by two- and three-component mixed-layer minerals. Clays and Clay Minerals, 48, 57–62.
Sakharov, B.A., Lindgreen, H., Salyn, A.L. & Drits, V.A. (1999) Determination of illite-smectite structures using multispecimen X-ray diffraction profile fitting. Clays and Clay Minerals, 40, 103–113.
Środoń, J. (1981) X-ray identification of randomly interstratified illite-smectite in mixtures with discrete illite. Clay Minerals, 16, 297–304.
Šuchá, V., Kraus, I., Gerthofferova, H., Petes, J. & Serekova, M. (1993) Smectite to illite conversion in bentonites and shales of the East Slovak basin. Clay Minerals, 28, 243–253.
Velde, B. & Brusewitz, A.M. (1982) Metasomatic and non-metasomatic low-grade metamorphism of Ordovician meta-bentonites in Sweden. Geochimica et Cosmochimica Acta, 46, 446–452.
Velde, B., Suzuki, T. & Nicot, E. (1986) Pressuretemperature- composition of illite/smectite mixedlayer minerals: Niger delta mudstones and other examples. Clays and Clay Minerals, 34, 435–441.
Watanabe, T. (1988) The structural model of illite/ smectite interstratified minerals and the diagram for their identification. Clay Science, 7, 97–114.
Weir, A.H., Ormerod, E.G. & El Mansey, I.M.I. (1975) Clay mineralogy of sediments of the western Nile Delta. Clay Minerals, 10, 369–386.


Related content

Powered by UNSILO

Composition variation of illite-vermiculitesmectite mixed-layer minerals in a bentonite bed from Charente (France)

  • A. Meunier (a1), B. Lanson (a2) and B. Velde (a3)


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed.