The effect of mechanochemical activation (dry grinding), formamide intercalation, and thermal deintercalation on high- and low-defect kaolinite surfaces was studied by thermogravimetry and diffuse reflectance Fourier transform infrared spectroscopy. These investigations were completed with specific surface area and pore size distribution measurements. The surface acidity of the ground and the ground-and-intercalated kaolinites was probed with ammonia adsorption. The surface area and the pore volume as well as the amount of adsorbed ammonia increased with the rate of mechanochemical activation. At the same time the thermally deintercalated minerals showed increased surface area but decreased pore volume with the time of grinding. Adsorbed ammonia was detected as ammonium ion in the 1400-1500 cm(-1) spectral range.