Illite/mica, distribution

The Lower Kittanning coal contains kaolinite (well-crystallized), illite/mica and expandable clays. Low total clay contents are observed in the center of the study area, where the coal is rich in pyrite, and in the north-central region where high quartz contents are observed. High total clay contents are seen on the northwestern and eastern margins of the basin. Because clay mineral data are presented as a percentage of the low-temperature ash, variations in the quartz and pyrite contents influence the proportionate distribution of the clays. To avoid this problem, the relative amounts of individual clay minerals in the clay (less than 2 micron) fraction were examined. As this size fraction contains only clays, variations in quartz and pyrite do not influence the results. 

In contrast to the homogeneous mica distribution in weakly podzolised sod-podzolic soils, higher illite contents and accumulation of expansible minerals have been found in a medium podzolised sod-podzolic soil by Labenets [1968]. In strongly podzolised acid soils, weathering of micas, especially of biotites, produces mixed-layered minerals, vermiculite, and soil mont-morillonite. These processes lead to a decrease of illite contents in the upper parts of the... 

If we now consider the bulk compositions of the mixed-layered minerals which contain both expandable and non-expandable layers, two series are apparent, one between theoretical beidellite and illite and one between theoretical montmorillonite and illite (Figure 25). The intersection of the lines joining muscovite-montmorillonite and beidellite-celadonite (i.e., expandable mineral to mica), is a point which delimits, roughly, the apparent compositional fields of the two montmorillonite-illite compositional trends for the natural mixed layered minerals (Figure 26). That is, the natural minerals appear to show a compositional distribution due to solid solutions between each one of the two montmorillonite types and the two mica types—muscovite and celadonite. There is no apparent solid solution between the two highly expandable (80% montmorillonite) beidellitic and montmorillonitic end members. The point of intersection of the theoretical substitutional series beidellite = celadonite and muscovite-montmorillonite is located at about 30-40% expandable layers— 70-60% illite. This interlayering is similar to the "mineral" allevardite as defined previously. It appears that as the expandability of the mixed... 

Illite. A group of three-layer, mica-like, and grey, light-green, or yellowish brown clay minerals, especially widely distributed in marine shales and soils derived from them of the general formula (H3O K)y(Al4.Fe4.Mg4,Mg6)(Si8 v.A1,)02o(OH)4, with y less than 2. 

Sea oil-source rocks, the mica-like component contains both K-rich end-member (illite) and NH4-rich end-member (tobelite) layers. The amount and the distribution of fixed K and NH4 was determined by a peak profile-fitting procedure on experimental powder (X-ray) diffraction features (Drits et al. 1997 Sakharov et al. 1999). 

Lanson B, (Champion D (1991) The I/S-to-illite reaction in the late stage diagenesis. Am J Sci 291 473-596 Lanson B, Kibler B (1994) Experimental determinations of the coherent scattering domain size distribution of natural mica-like phases with the Warren-Averbach technique. Clays Clay Minerals 42 489-494 Li G, Peacor DR, Merriman RJ, Roberts B (1994) The diagenetic to low grade metamorphic evolution of matrix white micas in the system muscovite-paragonite in a mudrock from Central Wales, U.K. Clays Clay Minerals 42 369-381... 

Some terrigenous clay minerals in recent sediments reflect both climatic and non-climatic influences. For instance, the distribution of illite (Figure 1), a mineral that primarily derives from the erosion of mica-bearing rocks, shows increased percentages in high latitude oceans due to predominant physical... 

The distribution of potassium in the B horizon clays of soils developed from loess in Nebraska, Iowa, and Illinois was studied by Wills and Riecken [1969]. The soils have been developed during the past 14,000 yr. Total potassium in the clay from the B horizon decreased from west to east, and this was in agreement with the theory that mica weathering is a function of the amount of rainfall. Although montmorillonite was the dominant clay mineral, there was relatively more illite in samples of higher potassium content and from sites receiving lesser amounts of precipitation. 

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