Hostname: page-component-77c89778f8-vsgnj Total loading time: 0 Render date: 2024-07-19T05:58:52.259Z Has data issue: false hasContentIssue false
  • English
  • Français

Order of Mixed-Layering in Illite/Montmorillonites

Published online by Cambridge University Press:  01 July 2024

John Hower
John Hower*
Affiliation:
Geology Department, Western Reserve University
Get access Rights & Permissions [Opens in a new window]

Abstract

A number of otherwise poorly understood compositional-structural relationships in mixed-layer illite/montmorillonites appear to be explained by ordered interlayering of 2:1 units. The ordering appears to be between high and low charge 2:1 units. The relationship between per cent expandable layers and mean lattice charge in natural materials shows a scatter that is nicely bracketed by hypothetical curves constructed assuming random or completely ordered interlayering for several types of 2:1 charge distribution. Natural samples with 30–50% expandable layers plotting near the “ordered” curves have diffraction peaks at 25 Å for two water layers in the expandable layers and 27 Å with two glycol layers; samples plotting near the “random” curves do not have these peaks and have poorly developed 001/001 reflections.

Some tentative conclusions are: (1) illites are virtually non-expandable at lattice charges significantly less than that of ideal mica because of ordering of high-low charge 2:1 units, (2) illites and mixed-layer illite/montmorillonites with the same mean lattice charge show a range of expandability because of varying degrees of ordering, (3) the highly variable CEC of samples with the same expandability also results from a varying degree of ordering.

An interesting petrological implication results when it is realized that a sample with a given bulk composition can have a wide range of expandability, depending on ordering. Low expandability, achieved by ordering, should be promoted by formation at high pressures. Glauconites, known to form largely at the time of sedimentation, appear to be dominantly randomly interstratified; illites and illite/montmorillonites, which may form on deep burial of argillaceous sediments, are dominantly ordered.

Type
Symposium on Mixed Layer Minerals
Information
Clays and Clay Minerals , Volume 15 , February 1967 , pp. 63 - 74
Copyright
Copyright © 1967, The Clay Minerals Society

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Burst, J. F. (1958) Mineral heterogeneity in “glauconite” pellets: Amer. Min. 43, 481–97.Google Scholar
Burst, J. F. (1959) Post diagenetic clay mineral environmental relationships in the Gulf Coast Eocene: Clays and Clay Minerals, Proc. 6th Conf., Pergamon Press, New York, 327–41.Google Scholar
Dunoyer de Segonzac, G. (1964) Les argiles du Crétáce Supérior dans le bassin de Douala (Cameroun). Problems de diagenèse: Bull. Serv. Carte geol. Als. Lorr. 17, no. 4, 287–310.Google Scholar
Hower, J. (1961) Some factors concerning the nature and origin of glauconite: Amer. Min. 46, 313–34.Google Scholar
Hower, J. and Mo watt, T. C. (1966) The mineralogy of illites and mixed-layer illite/ montmorillonites: Amer. Min. 51, 825–54.Google Scholar
Jackson, M. L. (1963) Interlayering of expansible layer silicates in soils by chemical weathering: Clays and Clay Minerals, Proc. 11th Conf., Pergamon Press, New, York, 29–46.Google Scholar
Jonas, E. C. (1960) Mineralogy of the micaceous clay minerals: Inter, Geol. Cong., XXI Sess., Part XXIV, 7–16.Google Scholar
MacEwan, D. M. C., Ruiz Amil, A. and Brown, G. (1961) Inter stratified clay minerals in The X-ray identification and crystal structures of clay minerals: Min. Soc. hond. 393–424.Google Scholar
Reynolds, R. C. (in press) Interstratified clay systems: Part I, Calculation of the total diffraction function.Google Scholar
Roberson, H. E. and Jonas, E. C. (1965) Clay minerals intermediate between illite and montmorillonite: Amer. Min. 50, 766–70.Google Scholar