Sericite (SE) and dehydrated sericite (dhSE) were examined using ion-exchange experiments with dodecylammonium (DDA) solutions of various initial concentrations (DDA(+)/K+ mole ratio = 1.0, 3.0, and 8.0) at 70 degrees C. A large basal spacing of 3.3 nm was observed for the dhSE complexes, which indicated the formation of a second-stage structure.