The phenomenon of colloidally induced fines migration is a challenge of both scientific and industrial importance. Its occurrence impacts permeability reduction and alteration of flow pathways in porous media, particulate contaminant migration in groundwater flow, and filtration. The release of smectitic fines is a threshold type of process resulting from discontinuous jumps, called microquakes in the interlayer spacing. There is a critical salt concentration at which these microquakes occur and produce fines migration in the porous media. The changes in the microstructure with decreasing salt concentration were analyzed using X-ray diffraction. The transition between crystalline and osmotic swelling regime is also shown to depend on the type of cation. A mathematical model developed using colloidal principles predicts the swelling behavior of smectites in aqueous solutions. The model can predict the transition of swelling from crystalline to osmotic regimes and explain the effect of different cations on the transition.