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

Abstract

Abstract-Three gels of illitic composition having different octahedral substitutions were hydrothermally treated in distilled water at 3000C and 500 bars for 7 to 90 days. The gel of the composition Ko.TAI2 o(Si~ 3Alo.00~o(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 US in the same run.Illitic gel having the composition Ko.~(AI L7Fe3+o.3)(Si3.3Aio.7)O~o(OH)2 having octahedral Fe 3+ substitutions yielded more and better crystalline I/S. The reaction products of the 7-35-day runs consisted mainly of randomly interstratified US having an expandability of 90 to 65%. The US particles occurred as foliated or compact tameilar aggregates having a smectite-like morphology, as described above. The Fe3+-bearing gel yielded, after 90 days of ageing, an Rl-ordered US having 25% expandability and a morphology of ribbons and hexagonal platelets.Illitic gel of composition Ko.s(mlt.6Mgo.4)(Si3.6Alo.4)Olo(Oa) 2 having octahedral Mg 2+ substitutions produced no illite even after 90 days of ageing, but a pure smectite in the form of foliated aggregates.

Mica Structure and Fibrous Growth of Illite

“…For this purpose, fine albite p o w d e r s were subjected to a hydrothermal alteration with KC1 solutions at 200~ bar for 2 4 -84 d. Negligibly small quantities of fibrous illite were found as accessories to large amounts of lamellar (platy) illites under neutral pH conditions. Later, C h a m p i o n (1989) synthesized both laths and lamellar illites using K-Si-A1 gels under hydrothermal conditions at 300-350~ and 12 kbar for 1 4 -3 2 d. The effects of octahedral substitutions of M g 2+ or Fe 3 § for A1 on illite morphology were studied by Giiven and Huang (1991). For this purpose, first the glasses were made from gels with the appropriate chemical c o mposition and then these glasses were subjected to hydrothermal alterations at 300~ and 500 bar for 3 5 -90 d. These experiments yielded large amounts of illite-smectite mixed layers (I-S) in the f o r m of foliated flakes and compact lamellar (platy) aggregates.…”

An Experimentally Derived Kinetic Model for Smectite-to-Illite Conversion and Its Use as a Geothermometer

“…Many experiments have been carried out to convert smectite to illite or US hydrothermally. Most of these experiments were designed to focus on a variety of special problems such as conversion rates (Eberl and Hower, 1976), the effect of interlayer cations (Eberl, 1978), octahedral substitution (Giiven and Huang, 1991), tetrahedral substitution (Huang and Otten, 1987), solution chemistry (Roberson and Lahann, 1981), kinetics of layer charge development (Howard and Roy, 1985), control of ordering of mixed-layers (Eberl, 1977;Inoue and Utada, 1983;Huang, 1989), conversion mechanism (Whitney and Northrop, 1988), and the effect of flow rate in flow through experiments (Kacandes et aL, 1991).…”

Hydrothermal synthesis of ammonium illite

“…The source of ammonium is unclear in hydrothermally altered volcanoclastic rocks (Kozác et al 1977; Higashi 1982;Bobos et al 1995). Variable geological environments and the effect of parameters such as temperature, time, fluid, and solid composition on illite and illite-smectite formation have been investigated in many hydrothermal experiments (e.g., Eberl and Hower 1977;Eberl 1978;Roberson and Lahann 1981;Inoue 1983;Whitney and Northrop 1988;Güven and Huang 1991;Huang 1992;Eberl et al 1993), but we * E-mail: sucha@fns.uniba.sk found only one paper that focused on experimental ammonium illite formation (Shigorova et al 1981).…”