Phyllosilicate clay minerals

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). 

Manceau A, Calas G (1987) Absence of evidence for Ni/Si substitution in phyllosilicates. Clay Minerals... 

Classification Scheme of Phyllosilicate Clay Minerals (T = Tetrahedral, O = Octahedral)... 

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). 

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. 

Although many authors insist upon the sequential degradation of phyllosilicates, i.e., taking the same initial material and transforming it into the various types of expandable minerals in the weathering process, (Heaver and Jackson, notably) this is undoubtedly not the only mechanism by which these clay minerals are formed in soils and possibly not the dominant one. Studies on the weathering of granites and more basic rocks... 

Let us now combine the zeolite phases related in Figures 32a-c with those phyllosilicates commonly found in the larger K-Na-Al-Si system. Representation of the clay minerals associated with zeolites can be made... 

Na and Ca to play equivalent roles in zeolites, as well as K, and if we consider A1 and Si as the major variables combined with K and Na in the phyllosilicates, we can adequately represent the phases in a (Ca-Na)-K-Al-Si system where H O is in excess in the fluid phase. If the system has four chemical variables and the natural assemblages are frequently found to contain four authigenic minerals, we must assume that most chemical variables are inert or extensive variables of the chemical system which controlled the crystallization of the zeolite-clay mineral containing sediments. ... 

CLAYS. The terms chy or cloys commonly refer to cither rocks that are consolidated or unconsolidated sediments, nr a group of minerals having unique properties. Traditionally, clays (rocks) are distinctive in al least two properties that render them technologically useful plasticity and composition. Clays are predominantly composed of hydrous phyllosilicates. referred to as clay minerals. These are hydrous silicates of Al. Mg. K, anti He. and other less ahundanl elements. Clay minerals arc extremely fine crystals or particles, often colloidal in size and usually plate-like in shape. The nonclay mineral portion of clays (rocks) may consist of other minerals, portions of rocks, and organic compounds. 

Bleam, W.F (1990). The nature of cation-substitution sites in phyllosilicates. Clays Clay Miner., 38 527-536. 

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