Illitic mica

Whitehouse and McCarter (23, 24), however, have shown some clear-cut evidence from laboratory experiments. Even if one wished that they had changed their sea water regularly, they did analyze their various products thoroughly. They found that fresh-water illite brought into sea water underwent rapid ion exchange (75% completed within 24 hours) but that it remained illite (mica) and that no new phase could be found even after five years. The same was true for kaolinite—i.e., ion exchange, 90% completed within 24 hours, but no new phase. 

The major mineral components of this coal are quartz, pyrite (and marcasite), and clays (predominantly kaolinite and illite/mica, with minor amounts of expandable clays). 

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. 

To examine further the influence of peat-swamp chemistry on the clays, the composition of the clay fraction of the coal samples was compared to that of floor, roof, and parting samples. Coal samples tend to be enriched in kaolinite compared to other sample types (Table I). Floor rocks tend to have the highest expandable clay contents, whereas roof rocks have the highest illite/mica contents. 

If it is assumed that the composition of the roof shales is the closest representation of parent mineralogy available, the clay sediments entering the depositional basin included considerable amounts of illite/mica, moderate amounts of kaolinite, relatively small amounts of expandable clays, and some chlorite. Whereas some modifications may have taken place since deposition of the clays in the roof shales, they probably have been affected less by the organic acids than the clays in the underclays, coals or partings. The presence of chlorite in the roof rocks suggests that acidic... 

Acidic conditions within the peat swamp, particularly in the freshwater areas, would favor the formation and/or preservation of kaolinite. This would result in the observed enrichment in kaolinite within the coal relative to the surrounding sediments. Relatively low illite/mica contents are observed in the coals, possibly due to alteration of this clay to expandable clays and ultimately to kaolinite. The transition from expandable clays to kaolinite has been observed in the Snuggedy Swamp by Staub and Cohen (JA). 

The most significant control on clay mineral composition, therefore, appears to be chemical conditions within the swamp which produced alteration of a parent material that included illite/mica, kaolinite, and lesser amounts of chlorite and expandabe clays. 

Chemical conditions within the peat swamp influenced the clay mineral assemblage. Kaolinite is enriched towards the margins of the depositional basin an authigenic origin in acidic freshwater conditions is proposed for much of this clay. Illite/mica is primarily detrital, as indicated by the presence of the... 

The 2 1 layer type has two tetrahedral sheets sandwiching an octahedral sheet. The three clay groups with this structure are (illitic) mica, vermicu-lite, and smectite (montmorillonite), each with the general unit cell chemical formula ... 

The structural similarity in illitic mica, vermiculite, and smectite minerals was noted in Sec. 1.1 (Table 1.3). The basal planes of these minerals are... 

Typical results of specific surface area determinations on phyllosilicates by nitrogen gas/water vapor or nitrogen gas/CPB adsorption are listed in Table 1.7. For Mg-vermiculite and Na-montmorillonite, the measured adsorption specific surface area is close to that calculated from the unit cell dimensions and structural formula. For illitic mica, the area is about 14 per cent of the ideal crystallographic value, indicating that this mineral forms particles containing about seven phyllosilicate layers that cannot be penetrated by water vapor or CPB. 

Table 1.8 lists specific surface area values for illitic micas as determined by nitrogen gas adsorption and by negative chloride adsorption.The specific surface areas calculated from N2 gas adsorption with the help of Eq. 1.7 show no particular trend with type of exchangeable cation. The mean value of 5, 11.2 0.5 x 10 m kg", suggests that the mineral forms particles containing seven phyllosilicate layers, as indicated previously. The external surfaces of these particles are expected to repel anions, and therefore the specific surface area determined by negative chloride adsorption should also be around lO m kg" . As shown in Table 1.8, however, the values of 5k, obtained with Eq. 1.18, are always less than 5 and decrease sharply with increasing radius of the... 

Table 1.8. Specific surface areas of illitic micas and montmorillonites determined by N2 gas adsorption (5n) and chloride exclusion (5e) ...

C. E. Weaver and L. D. Pollard, The Chemistry of Clay Minerals. Elsevier, Amsterdam, 1973. The term illitic mica refers to a dioctahedral micaceous mineral weathered in soil. 

See, e.g., D.M.C. MacEwan and M. J. Wilson, Interlayer and intercalation compounds of clay minerals, in G. W. Brindley and G. Brown, op cit. That 1 1 electrolytes cannot be dissolved completely in adsorbed water on smectites and illitic micas has been shown by A. M. Posner and J. P. Quirk, The adsorption of water from concentrated electrolyte solutions by montmorillo-nite and illite, Proc. Royal Soc. (London) 278A 35 (1964). 

Illite Mica like clay mineral Triclinic Translucent... 

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