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Effects of Octahedral Mg2+ and Fe3+ Substitutions on Hydrothermal Illitization Reactions

Published online by Cambridge University Press:  02 April 2024

Necip Güven  and
Wuu-Liang Huang
Necip Güven
Affiliation:
Department of Geosciences, Texas Tech University, P.O. Box 4109, Lubbock, Texas 79409
Wuu-Liang Huang
Affiliation:
Exxon Production Research Company, Houston, Texas 77001
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Abstract

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Three gels of illitic composition having different octahedral substitutions were hydrothermally treated in distilled water at 300°C and 500 bars for 7 to 90 days. The gel of the composition K0.7Al2.0(Si3.3Al0.7)O10(OH)2, having no octahedral substitutions, yielded poorly crystalline and randomly interstratified illite/smectite (I/S) having possibly 30% or more expandability. These I/S particles occurred predominantly as foliated or compact lamellar aggregates having morphological features characteristic of common smectite. Laths having a morphology similar to that of diagenetic “fibrous illites” were also found in small amounts after the gel had been aged for 35 days. Their chemical composition was similar to that of the foliated aggregates of I/S in the same run.

Illitic gel having the composition K0.7(Al1.7Fe3+0.3)(Si3.3Al0.7)O10(OH)2 having octahedral Fe3+ substitutions yielded more and better crystalline I/S. The reaction products of the 7-35-day runs consisted mainly of randomly interstratified I/S having an expandability of 90 to 65%. The I/S particles occurred as foliated or compact lamellar aggregates having a smectite-like morphology, as described above. The Fe3+-bearing gel yielded, after 90 days of ageing, an Rl-ordered I/S having 25% expandability and a morphology of ribbons and hexagonal platelets.

Illitic gel of composition K0.8Al1.6Mg0.4)(Si3.6Al0.4)O10(OH)2 having octahedral Mg2+ substitutions produced no illite even after 90 days of ageing, but a pure smectite in the form of foliated aggregates.

Keywords

Illite/smectiteIllitizationInterstratificationOctahedral substitutionSynthesis
Type
Research Article
Information
Clays and Clay Minerals , Volume 39 , Issue 4 , August 1991 , pp. 387 - 399
Copyright
Copyright © 1991, The Clay Minerals Society

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