CLAY MINERALSClay minerals have a layer structure, each layer is composed of silica and alumina sublayers or sheets. Within the Si sheet, each silicon ion is surrounded by four oxygen ions — comprising a tetrahedron (Tetrahedral Sheet).
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•The metallic ion in these sheets can vary, i.e., Si4+, Al3+, Mg2+, or Fe2+•These can be replaced with similar size cations,--That is Al3+ can replace Si4+.• This is called isomorphous substitution. This results in a negatively charged clay surface. The surface charge varies depending on the type of clay present in a soil.CLAY MINERALS (cont.)Within the Al sheet, each aluminum ion is surrounded by six hydroxyl (OH) ions comprising an octahedron (Octahedral Sheet).