Mineral Names and Structures

In order to avoid confusion or misunderstanding, it is necessary to define the major terms which will be used in the following discussions. 

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. 

It is useful as a point of departure, to briefly describe the basic crystal lattice common to phyllosilicates. The elementary character is the SiO tetrahedral linkage of an essentially two-dimensional, hexagonally symmetric, network. One side of this sheet network is coordinated with other cation-oxygen complexes joined by an important component of covalent bonding while the other is coordinated by essentially ionic bonding or van der Waals type bonds. The key to phyllosilicate structures is the oxygen network which determines the shape and extent of the structure. 

A superficial classification of the most common clay mineral groups can be based upon the number of ions present in the octahedral layer (2 diocatahedral or 3 trioctahedral) and the numbers and the kind of ions 

It is important to note that the clay minerals which have an interlayer charge between 1.0 and 0.7 contain almost exclusively potassium as an interlayer ion. In minerals with a lower charge 0.6-0.25 a large charge is less, no alkali or alkaline earth elements are present. 

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