The dissolution rate of natural barite cleavage fragments was measured in deionized water and NaCl brines over the temperature range 44-85°C. Dissolution followed first-order kinetics, with an activation energy of 24.9 ± 10.1 kJ/mol. The observed insensitivity to stirring rate and low absolute value of the rate constant (extrapolated k at 25° C = 3.30 ± 1.31 × 10 -3L/ m2s) indicated desorption rather than volume diffusion as the rate-determining step. The NaCl concentration had no effect on k up to 0.1 M. Barite growth from supersaturated aqueous solutions was also studied. Precipitation followed a second order rate law, k25° C = 162 ± 65 L2/ sm2mol, Ea = 22.0 ± 14.3 kJ/mol, and was not sensitive to pH variation. A different rate law is likely to apply at high supersaturations, where a change in secondary growth morphology was observed.