Clays phyllosilicates

Disaggregation zones are formed where no or little grain fracturing occurs during the deformation (Fig. 2h). These can develop as deformation bands in unlithified or poorly consolidated lithologies and in general do not form effective barriers to flow in sandstones with clay/phyllosilicate contents below -15%. 

Layered materials are of special interest for bio-immobilization due to the accessibility of large internal and external surface areas, potential to confine biomolecules within regularly organized interlayer spaces, and processing of colloidal dispersions for the fabrication of protein-clay films for electrochemical catalysis [83-90], These studies indicate that layered materials can serve as efficient support matrices to maintain the native structure and function of the immobilized biomolecules. Current trends in the synthesis of functional biopolymer nano composites based on layered materials (specifically layered double hydroxides) have been discussed in excellent reviews by Ruiz-Hitzky [5] and Duan [6] herein we focus specifically on the fabrication of bio-inorganic lamellar nanocomposites based on the exfoliation and ordered restacking of aminopropyl-functionalized magnesium phyllosilicate (AMP) in the presence of various biomolecules [91]. 

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

The clay minerals can now be discussed in terms of their relationship with the phyllosilicates (sheet silicates). It is important to keep clearly in mind here the difference between clay - the material which is dug out of the ground, and which may be a mixture of different clay minerals, together with various nonclay minerals (such as quartz, pyrite, etc), as well as unaltered rock fragments and incorporated organic material (Grim, 1968) - and the clay minerals themselves, which are crystalline compounds of specified stoichiometry and structure. At this stage, we are only considering the structure of the clay minerals. 

Brown, G. (1984). Crystal structure of clay minerals and related phyllosilicates. In Clay Minerals Their Structure, Behaviour and Uses, ed. Fowden, L., Barrer, R.M. and Tinker, P.B., Royal Society, London, pp. 1 20. 

Extremely high ion exchange affinities are however sometimes observed for alkali metals (e.g. Cs) and transition metal ion complexes in clay minerals and zeolites. The objective of this paper is to give an account of the factors which are involved in these high selectivity phenomena. The discussion will be focussed mostly on montmorillonites and faujasites as representatives of the phyllosilicate and tectosilicate groups. 

A1 uminosil icate mim ral s. Standard free energies of Ca - 2K exchange, aG, were always negative, showing that all of the 2 1 phyllosil icate minerals (hereafter described simply as clays) studied, and the 1 1 mineral, kaolinite, were selective for K over Ca (Table I). 

Phyllosilicates are clay-related compounds with a sheet structure such as talc, mica, kaolin, etc. for which the nucleation mechanism of PET is known to be heterogeneous, although still uncertain. 

Crovisier, J. L., Vernaz, E., Dussossoy, J. L. Caurel, J. 1992b. Early phyllosilicates formed by alteration of R7T7 glass in water at 250°C. Applied Clay Science, 7, 47-57. 

After the experiments, significant quantities of newly formed minerals were observed at the cold extremity of the tube, pointing to a fast material transport by diffusion from the hot to the cold end of the tube. The following spatial distribution of newly formed phases, reflecting the temperature profile, was observed in both runs (Fig. 8) quartz + K-feldspar + plagioclase + Mg-rich saponites (hot extremity) quartz + K-feldspar + plagioclase (middle of the tube) and alkaline or Ca-rich clays + quartz + plagioclase (cold extremity). The cation composition of the phyllosilicates was similar in both experiments. Some newly fonned quartz crystals... 

Phyllosilicates (clay minerals) - layered silicates such as Al4Si4O10(OH)8 (kaolinite) and (Ca,Na)o.7(Al,Mg,Fe)4(Si,Al)802o(OH)4.nH20 (montmorillonite, also called smectite). 

Clays are layer silicates (phyllosilicates) of particle size less than about 4 pm, produced by the weathering of aluminosilicate rocks. Clay minerals fall roughly into two structural classes the kaolinite type, based on paired sheets of tetrahedral (SiC>44-) and octahedral [A10n(0H) g " or... 

It should be possible, through a unification of chemical and mineral structure data and the results of experimental studies on silicate phase equilibria, to develop a general picture of clay mineralogy based upon the known chemical behavior of phyllosilicates under various physical conditions. The major elements for such a study are presently available in a rough outline. It is fact the purpose of this essay to summarize the available information and create a general outline of clay mineral petrology. It is hoped that such an attempt meets with some success and, more important in the long run, that such an attempt will interest others in similar exercises, especially those of precision and revision. 

No new definitions will be proposed here but a simple outline of the basic vocabulary is given which will be used to permit a discussion of the problems of physical chemistry of phyllosilicates and other silicate minerals found in clay mineral suites. 

The following pages give a review of the chemistry of natural minerals, their typical occurrence in nature and their common mineral associations. This review is used to establish the major groupings of the common clay mineral species as a function of the chemical systems to which they can be related. Because various forms of silica as well as zeolites and organic materials are commonly associated with clays, these materials have been considered in the same manner as the phyllosilicates. It is evident that they have an influence on the clay mineralogy and that they form an integral part of clays in the broad sense of the term. However, they are not normally considered to be clay minerals. 

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