Divalent tin has been intercalated into montmorillonite by reacting partially hydrolyzed solutions of SnCl 2 under aerobic conditions at pH = 2.8 with aqueous dispersions of the smectite mineral. The precursor tin solution contains mainly the cationic trimeric ion Sn 3 (OH) 4 (super 2+) , which is shown to take part in the exchange reactions with the surface cations of the mineral. Variable temperature Mossbauer spectroscopy was used in order to: 1) directly probe changes in the oxidation state and coordination environment of Sn 2 in the process of intercalation; 2) examine the nature of tin atoms on the external surfaces and in the interlayer space of the clay platelets; and 3) study the dynamics of motion of tin atoms on the clay surfaces. The main conclusion from these studies is that about 75% of the Sn (super 2-) ions undergo extensive oxidation to the +4 state with concomitant hydrolysis and condensation that lead to the precipitation of SnO 2 on the external surfaces of the clay. The rest of the Sn (super 2+) ions are introduced into the lamellar zone, as evidenced by the detailed Mossbauer analysis of the dynamics of motion of tin atoms on the clay surfaces.