Carbonate Clay: Measurement and Relationship to Clay Distribution and Cation‐Exchange Capacity

A method for the determination of carbonate clay as an integral part of the pipette method for particle‐size analysis is given. Carbonate clay is calculated by measuring the gravimetric loss of CO2from a 50‐ml. aliquot of the clay (< 2µ) fraction. For some calcareous soil materials a substantial proportion of the clay fraction consists of carbonate. A survey is given of the proportion of carbonate that is claysize. Five kinds of clay percentages for calcareous soil materials are discussed. The application of carbonate clay data to the interpretations of clay distribution curves is presented. Evidence is presented that carbonate, including carbonate clay, has negligible cation‐exchange capacity. The effect of the presence of carbonate clay on the calculated cation‐exchange capacity of the clay fraction is discussed.