Muscovite mica was delaminated by heating with concentrated lithium nitrate solution. The delamination occurred through partial replacement of the alkali counterions originally present by lithium. The H+/Li+ exchange was studied in dilute nitric acid. With delaminated mica it was possible to follow the ion exchange by measuring the change in conductivity of the reaction mixture. The exchange was also followed by measuring the amount of released lithium and was found to be fast. When the adsorbed lithium ions were replaced by potassium, the mica platelets collapsed to stacks with lower accessible surface area, and the ion exchange capacity was reduced to one-fifth of the original value. This was attributed to the smaller short-range repulsive (hydration) forces of the potassium ions. The H+/K+ exchange on delaminated mica was slower than the corresponding H+/Li+ exchange and its equilibrium constant was much smaller than that of the H+/Li+. The affinity of oxonium ions to the muscovite surface is much higher than that of lithium but is comparable to that of potassium.