Illite definition

Fig. 4.18 shows the result of Cd2+ adsorption on illite in presence of Ca2+ (Comans, 1987). The data are fitted by Freundlich isotherms after an equilibration time of 54 days. It was shown in the experiments leading to these isotherms that adsorption approaches equilibrium faster than desorption. Comans has also used 109Cd to assess the isotope exchange he showed that at equilibrium (7-8 weeks equilibration time) the isotopic exchangeabilities are approximately 100 % i.e., all adsorbed Cd2+ is apparently in kinetic equilibrium with the solution. The available data do not allow a definite conclusion on the specific sorption mechanism. 

During the process of lithification and deep burial illite appears to remain stable or at least is slow to react with other minerals. It is by far the most dominant species of clay mineral in argillaceous sedimentary rocks (Grim, 1968 Millot, 1964). In early burial, the overall illite content of a specimen may decrease during adjustment to bulk chemical and physical restraints (Perry and Hower, 1970) however most studies of deeply buried sediments show a definite increase in illite as pressures and temperatures increase (Millot, et al., 1965 Dunoyer de Segonzac, 1969 ... 

Mixed-layer illite-montmorillonite is by far the most abundant (in the vicinity 90%) mixed-layer clay. The two layers occur in all possible proportions from 9 1 to 1 9. Many of those with a 9 1 or even 8 2 ratio are called illites or glauconites (according to Hower, 1961, all glauconites have some interlayered montmorillonite) and those which have ratios of 1 9 and 2 8 are usually called montmorillonite. This practice is not desirable and js definitely misleading. Other random mixed-layer clays are chlorite-montmorillonite, biotite-vermiculite, chlorite-vermiculite, illite-chlorite-montmorillonite, talc-saponite, and serpentine-chlorite. Most commonly one of the layers is the expanded type and the other is non-expanded. 

The layers may be regularly or randomly interstratified. The latter are by far the more common and are probably the second most abundant clay mineral species, following illite (which in most cases is a mixed-layer clay). More regularly interstratified clay minerals have a definite periodicity and some are given specific mineral names. The randomly interstratified clay minerals are described in terms of the type and proportion of the two or more types of layers. Many of them exhibit some degree of regular interlayering. 

It is common practice to make a distinction between the inorganic constituents of so-called "Eastern" and "Western" coals By definition. Western coals are those for which the CaO+MgO content exceeds the Fe203 content of the ash, while the reverse is true for Eastern coals [ 1 I The inorganic constituents in Eastern coals, which are principally bituminous in rank, are predominantly in the form of discrete mineral particles. Clay minerals (kaolinite, illite) are usually dominant, followed by quartz and pyrite. The range and typical values of the mineral distribution and ash chemistry of Eastern coals are shown in Table I. These data were determined from computer-controlled scanning electron microscopy (CCSEM), Mossbauer spectroscopy, and other measurements on over a hundred coals. 

Kisch HJ (1987) Correlation between indicators of very low-grade metamorphism. In Low Temperature Metamorphism. M Frey (ed) Blackie and Son, Glasgow, p 227-300 Kisch HJ (1990) Calibration of the anchizone A critical comparison of illite crystallinity scales used for definition. J Metamor Geol 8 31-46... 

Results of models for the Tournemire shales are reported in Table 4. These models were based upon the mineralogical and CEC data presented in Tables 1 and 2 the calculated cation exchange selectivity coefficients and the concentrations of leachable Cl present in the rocks. Preliminary selectivity coefficients (Ac(Mg/Na) and Kc Ca./ Na) close to 3 and 4 respectively) have been derived from aqueous extraction experiments. They are in rather good agreement with literature data (Baeyens Bradbury 1994), and are mainly related to the illite and inter-stratified illite/smectite contents. The leachable Cl has been extracted with pure water at a liquid/solid ratio of 10mlg. It is clear that the Tournemire porewater cannot be definitively described with the data available. The porewater is of Na-Cl-(HCO ) type, with a low salinity, equivalent to a total dissolved... 

Von Engelhard et al [1962] have reported dioctahedral chlorite, mixed with quartz, kaolinite, and considerable interstratified illite-montmorillonite, in clay-marl sediments of the middle Keuper of Wurttemburg. The material does not expand on solvation. The rf(060) values for all the clay components are between 1.490 and 1.504 A. The tetrahedral Al content is 1.1 atoms, judged by the stated definitely whether the chlorite has two dioctahedral sheets or mixed di,tri-octahedral sheets. The 001 reflection at 14.23 A intensifies on heating at 550°C and decreases in spacing to 13.73 A. The interlayer material appears to be unstable, because /(OOl) decreases further to 11.9 A on heating to 700°C. 

As regards the illitic or, as Martin Vivaldi and MacEwan [1957] have termed it, the zoned type of interstratification (which typically gives a sharp peak with associated diffuse diffraction on one side of the peak), no exact calculations have been made, and it is only possible to make qualificative estimates regarding the nature of the material. MacEwan and Ruiz-Amil [1966] have assumed that in minerals of this type, there is not a definite probability of succession of layers, but rather a probability defined as p(d), that layers of intercalated... 

Total K analysis suggests the presence of 25% illite in the Monticello medium clay, although no definite 10 A peak is seen on the X-ray diffraction pattern the Billings clay, with 45 % illite, does show such a maximum. 

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