Illite organic complexes

The features of the adsorbed complex of the Cambrian argillites were intensely transformed by diagenetic reactions, making them unsuitable for any interpretations. The complex composition of the clays which consist of kaolinite, illite, chlorite and mixed-layer minerals, together with the absence of organic matter leads to the conclusion that the areas of denudation must have been of a local nature. At the same time, we may reconstruct a temperate to humid climate interrupted at times by periods of relative aridity. This explains the lack of laterites on the eruptive and metamorphic rocks. 

Clays with mica-type lattices, especially vermiculite and illite, can also react with many organic compounds to form complexes in which the organic substance is held in the clay lattice. The rate of reaction with vermiculite is fairly rapid but very slow with illite and mica. Differences in behavior of these minerals has been attributed to surface area and to the density of charge on the surface. 

Another member of the illite group is hydrous mica, in which the principal interlayer cation is K. A smectite you might encounter is montmorillonite smectites can expand by incorporating water or organics between the structural layers. Vermiculite is derived from the Latin vermiculare, which means to breed worms, and describes what appears to happen when the material is heated rapidly. Otherwise it is very similar to phlogopite mica. As you would guess, most of these minerals have complex chemical compositions. 

Figure 5.8 Analysis of the infrared spectrum of a mineral, (a) Sample spectrum 50% albite (k-feldspar) 23% siderite 17% illite 10% chlorite, (b) Calculat spectrum 49.7% feldspar (8.0% albite, 13.2% orthoclase and 28.5% microcline) 25.2% siderite 19.0% illite 6.8% chlorite, (c) Residnal difference spectrum. From Brown, J. M. and Elliot, J. J., The Quantitative Analysis of Complex, Multicomponent Mixtures by FTIR the Analysis of Minerals and of Interacting Organic Blends , in Chemical, Biological and Industrial Applications of Infrared Spectroscopy, Durig, J. R. (Ed.), pp. 111-125. Copyright 1985. John Wiley Sons Limited. Reproduced with permission.

Red clays used for the manufacture of terra cotta products are actually natural mixtures with a complex composition. They generally contain kaolinite, illite and/or other clays rich in alkaline, sand, mica (formula Si3Al3Oi0(OH)2), goethite (FeO(OH)) and/or hematite (Fe203), organic matter and, very often, calcium compounds. The latter, just like the micas and the other alkaline-rich compounds, help lower the firing temperature of the shard. 

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