Layer Charge of the Expandable Component of Illite/Smectite in K-Bentonite as Determined by Alkylammonium Ion Exchange
—The charge of the expandable interlayers in a series of fourteen diagenetic illite/smectites (I/S) from lower Paleozoic K-bentonites was determined by the alkylammonium ion exchange method. The magnitude (<0.50 equivalents per half formula unit) and characteristic heterogeneous distribution of interlayer charges in eight samples with expandabilities from 70% to about 15% confirm the smectitic character of the expandable interlayers in this range. This result coupled with the lack of a correlation between expandability and interlayer charge is consistent with the hypothesis of a layer-by-layer transformation from a precursor smectite to highly illitic I/S clays during K-bentonite diagenesis. The charge of the expandable interlayers in I/S samples with about 10% or less expandabilities have been inferred to be vermiculitic rather than smectitic. The K-fixed interlayers and expandable interlayers in these samples appear to be similar in charge. The significantly higher charges inferred for the highly illitic samples can be consistent both with a layer-by-layer transformation and the neoformation mechanisms proposed in the literature for the formation of illite.
Key WordsAlkylammonium Bentonite Clays Diagenesis Illite Illite/smectite Layer charge Smectite
Unable to display preview. Download preview PDF.
- Altaner, S. P., and C. M. Bethke. 1988. Interlayer order in illite/smectite. Amer. Miner. 73: 766–774.Google Scholar
- Cetin, K. 1992. The nature of illite/smectite clays smectite illitization in Paleozoic K-bentonites. Ph.D. dissertation. University of Cincinnati, Cincinnati, Ohio, 200 pp.Google Scholar
- Lagaly, G., and A. Weiss. 1969. Determination of layer charge in mice-type layer silicates. Proceedings of the International Clay Conference, Tokyo, Japan, L. Heller, ed. 61–80.Google Scholar
- Lagaly, G., and A. Weiss. 1976. The layer charge of smectitic layer silicates. Proceedings of the International Clay Conference, Mexico City, Mexico, 1975, 157–172.Google Scholar
- MacEwan, D. M. C. 1958. Fourier transform methods for studying scattering form lamellar systems: II. The calculation of x-ray diffraction effects for various types of inter-stratification. Kolloidzeitschrift 156: 61–67.Google Scholar
- Moore, D. M., and R. C. Reynolds Jr. 1989. X-ray diffraction and the identification and analysis of clay minerals. Oxford: Oxford University Press, 332 pp.Google Scholar
- Reynolds, R. C. Jr. 1980. Interstratified clay minerals. In Crystal Structure of Clay Minerals and Their X-ray Identification. G. W. Brown and G. Brown, eds. London: Mineralogical Society, 249–303.Google Scholar
- Reynolds, R. C. Jr. 1985. NEWMOD: A computer program for the calculation of one-dimensional diffraction patterns of mixed-layer clays. R. C. Reynolds, 8 Brook Rd., Hanover, NH, 24 p.Google Scholar
- Weaver, C. E., and L. D. Pollard. 1973. The Chemistry of Clay Minerals. Amsterdam: Elsevier, 250 pp.Google Scholar