Isomorphic substitution description

Aluminosilicates such as montmorillonite, kaolinite, illite, and vermiculite are solids that have structures readily accessible to counter ions. The excess negative charge resulting from isomorphic substitution of Al for Si is primarily distributed over the three adjacent surface O atoms of the layer, where it is electrically balanced by mobile, exchangeable cations- Thermodynamically, ion exchange can be interpreted in terms of the interlayer electrostatic interaction between surface charges and hydrated cations in accordance with the classical Eisenman theory (Eisenman, 1983). A comprehensive description has recently been given by Maes and Cremers (1986). 

Foster s studies really represent a broad correlation of the descriptive mineralogy and structural chemistry of the mica group. The limits appear to be fully compatible with the stresses and strains that are thought to develop within the crystal structures of the micas as dilferent isomorphous substitutions occur (Radoslovich [1963b]). 

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