ABSTRACT
The most common clay minerals used in the manufacture of building materials are kaolin, illite (a micaceous clay) and montmorillonite, a more plastic clay of variable composition. Clay crystals are generally hexagonal in form and in pure kaolin the crystals are built up of alternating layers of alumina and silica (Fig. 8.2). However, in illite and montmorillonite clays, the variable composition produced by sedimentation produces more complex crystal structures.
