Smectite to illite reaction

Kim J, Dong H, Seabaugh J, Newell SW, Eberl DD (2004) Role of microbes in the smectite-to-illite reaction. Science 203 830-832... 

Lynch F. L. (1997) Frio shale mineralogy and the stoichiometry of the smectite-to-illite reaction— the most important reaction in clastic sedimentary diagenesis. Clays Clay Mire 45, 618-631. 

Huang et al. (1993) derive a rate equation for the smectite to illite reaction at low Mg + and low to moderate Na concentrations, which is... 

Tissot B, Durand B, Espitalie J, Combaz A (1974) Influence of nature and diagenesis of organic matter in formation of petroleum. Am Assoc Pet Geol Bull 58 499-506 Vandenbroucke M, Pelet R, Debyser V (1985) Geochemistry of humic substances in marine sediments. In Aiken G R, McKnight D M, Wershaw R L, MacCarthy P (eds) Humic substances in soils, sediments, and water. Wiley, New York, pp 249-273 Whitney G (1990) Role of water in the smectite-to-illite reaction. Clays Clay Minerals 38 343-350... 

The Michigan Basin brines very low pH helps to explain their ability to leach and react with other rocks, as is indicated by their high contents of strontium, barium and other metals, although much of the Sr and Ba probably came from the reaction with calcite. Geothermal water also probably mixed with some of the formations, as indicated by the variable presence of iodine, boron, lithium, cesium, rubidium and other rare metals. With most of the brines, the calcium concentration is somewhat higher than its magnesium equivalent in seawater end liquor from a potash deposit, and the potassium a little lower. Wilson and Long (1993) speculated that this occurred by the conversion of the clays kaolinite and smectite to illite ... 

The transformation of smectite to mixed layer smectite-illite, and ultimately to illite, with increasing temperature is an extremely important reaction in many sedimentary basins, including the northern Gulf of Mexico Basin (Hower et al., 1976 Boles and Franks, 1979 Kharaka and Thordsen, 1992). The water and solutes released and consumed by this transformation are major factors in the hydrogeochemistry of these basins, because of the enormous quantities of clays involved. Several reactions conserving aluminum or maintaining a constant volume have been proposed for this transformation (Hower et al., 1976 Boles and Franks, 1979). The reaction proposed below (Equation (4)) conserves aluminum and magnesium, and is probably a closer approximation based on the composition of formation waters in these systems ... 

The rate of the smectite - illite reaction is thus directly proportional to K"" and H+, but is retarded by and by dissolved silica and Na". In deepening sedimentary basins, the extent of the reaction at any depth also depends on the local thermal gradient (temperature) and the sediment burial rate (reaction time). Because smectites of small particle size are the least stable, they alter to illite at lower temperatures than do coarser-grained smectites (Fig. 9.5). 

Sorption depends on Sorption Sites. The sorption of alkaline and earth-alkaline cations on expandable three layer clays - smectites (montmorillonites) - can usually be interpreted as stoichiometric exchange of interlayer ions. Heavy metals however are sorbed by surface complex formation to the OH-functional groups of the outer surface (the so-called broken bonds). The non-swellable three-layer silicates, micas such as illite, can usually not exchange their interlayer ions but the outside of these minerals and the weathered crystal edges ("frayed edges") participate in ion exchange reactions. 

Shaking in water prior to each drying cycle speeds reaction. For example, a K-Kinney smectite subjected to 64 WD cycles produced 42% illite layers, with shaking, compared with 30% for K-Kinney subjected to 50 WD cycles, and 32% for K-Kinney subjected to 75 WD cycles, without shaking. 

The experiments also indicate that WD may be an important mechanism for producing I/S at low temperatures in nature by a transformation mechanism (56). The percentage of illite layers formed by this mechanism is proportional to the number of WD cycles, and to the layer charge of the original smectite. Simple K-exchange does not produce stable illite layers in smectite therefore, these layers probably form by WD prior to deposition in subaqueous environments. The exception is found in high pH environments where illite layers may form without WD by chemical reaction, as has been reported previously for alkaline lakes (64, 65). 

It is generally agreed on the basis of TEM evidence (e.g., Rask et ai, 1997) and on the basis of chemical substitution in the several structural sites of illite (e.g., Lanson and Champion, 1991 Awwiller, 1993 Lynch et ai, 1997) that the illitization of smectite, like other replacement reactions in late diagenesis, proceeds through a dissolution/precipitation mechanism. Similar to other replacement minerals, illite also occurs as cements in sandstones as well as in shales, where it forms overgrowths on detrital illite particles and discrete crystals (cements) (e.g., Lanson and Champion, 1991 Rask et at, 1997). 

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