R.T. Martin, S.W. Bailey, D.D. EBERL, D.S. Fanning, S. Guggenheim, H. Kodama, D.R. Pevear, J. Srodon, F.J. Wicks // Clays and Clay Minerals, Vol. 39, No. 3, pp. 333-335, 1991. Clay materials commonly contain a considerable fraction of layer silicate minerals that exert a strong influence on the nature of the material. Both the structural and chemical characteristics of the constituent layer silicates play a role in determining the extent of this influence. They are the fundamental features needed to explain the variations in properties of clay materials. Layer silicate minerals can be classified conveniently on the basis of these characteristics (Tables l, 2). Structural characteristics include, for example, the type of silicate layer or linkage configuration (for modulated layer silicates). Chemical characteristics include both the magnitude of net layer charge (x) per formula unit and the type of interlayer material. Obviously, structural features are interrelated with chemical characteristics Except for the micas, all hydrous layer silicate species are given in the Tables, even if they are not found as clay minerals. The classification scheme is expected to evolve as knowledge of the details of these minerals increases.