Stability of illite/smectite during diagenesis: an experimental study

Journal Article · Sat Aug 01 04:00:00 UTC 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90259-6· OSTI ID:5062906

Sass, B M; Rosenberg, P E; Kittrick, J A

Illites from Goose Lake (Illinois) and Beavers Bend (Oklahoma) were equilibrated in 0.2 M and 2.0 M KCl solutions with excess kaolinite and either gibbsite, boehmite, quartz, or amorphous silica. Teflon-lined reaction vessels were used to heat the charges from 25/sup 0/ to 250/sup 0/C at the vapor pressures of solution. Partial reversibility was demonstrated by approaching equilibria from both high and low K/sup +/H/sup +/ activity ratios. The experimental data were used to construct isothermal, isobaric activity diagrams (log (a/sub K/sup +//a/sub H/sup +//) vs. log a/sub SiO/sub 2//) for the system K/sub 2/O-Al/sub 2/O/sub 3/-SiO/sub 2/-H/sub 2/O. Stability regions have been defined for kaolinite, boehmite, and three other phases that are believed to be components of both illites. At low temperatures (<90/sup 0/C) illite-smectite equilibrium is metastable with respect to calculated kaolinite-microcline equilibrium. Between 90/sup 0/C and 110/sup 0/C a phase transition involving illite and smectite occurs which stabilizes the assemblages illite-smectite-kaolinite and illite-smectite-microcline. This transition occurs at the same temperature as the ordering transition in natural IS. Above 110/sup 0/C the assemblage illite-smectite is again metastable with respect to kaolinite-microcline, but at 200/sup 0/C and above illite and smectite may coexist stably with either kaolinite or microcline. However, smectite decomposes where a/sub SiO/sub 2//sup 0// is controlled to quartz solubility yielding the stable assemblage illite-kaolinite-quartz and illite-mica-quartz.

• Research Organization: Battelle, Pacific Northwest Labs., Richland, WA (USA)
• OSTI ID: 5062906
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 51:8; ISSN GCACA
• Country of Publication: United States
• Language: English

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