Samples of a mixture of Fe, Mg-chlorite and sericite, a Mg-chlorite, a Fe-chlorite, and a sericite were treated with 0.05N H₂SO₄ in a closed system at 25, 50, and 80°C for varying periods of time, and the susceptibility of the minerals to the treatment, in terms of dissolution of cations such as Si, Al, Mg, Fe, and K, has been investigated. The dissolution rate of the cations increased with temperature for all samples examined, and the rate was higher in the chlorites than in the sericite at all temperatures. The dissolution of the cations was incongruent, and the chlorites released Al, Mg, and Fe more rapidly than Si. It seemed, for the chlorites, that the cations in the interlayer and octahedral sheets were dissolved at a higher rate than those in the tetrahedral sheets. It was found also that the Fe-rich chlorite was more susceptible to the acid treatment than the Mg-rich one.