The determination is based on the difference in rates of solution of calcite and dolomite. The CO2 evolved from reaction of a mixture of calcite and dolomite in excess HCl is measured at frequent intervals until the reaction is completed. The logarithm of the amount of CO2 equivalent to unreacted carbonate is plotted against time. Following the rapid and complete solution of calcite, the curve for dolomite assumes a much smaller slope and is linear for a period of time. Extrapolation of this linear portion of the curve to zero time gives the amount of CO2 equivalent to the dolomite initially present. The CO2 from calcite is obtained by difference from the total CO2. The amounts of calcite and dolomite found in a number of prepared mixtures by this intercept method were in good agreement with the amounts known to be present. Several samples of limestone and calcareous soil were analysed by the proposed method and the results were compared with X-ray diffraction and chemical data.