Provided herein are various embodiments of determining a cation exchange capacity of a rock sample. One embodiment of a method of determining a cation exchange capacity of a rock sample comprises equilibrating the rock sample to a relative humidity, performing a dielectric permittivity measurement on the rock sample at the relative humidity, and determining a cation exchange capacity of the rock sample based on the dielectric permittivity measurement. One embodiment of a method of determining a cation exchange capacity of a rock sample comprises receiving a dielectric permittivity measurement on the rock sample, and determining a cation exchange capacity for the rock sample based on the dielectric permittivity measurement of the rock sample and a relationship between cation exchange capacity and dielectric permittivity measurements for mineral mixtures corresponding to a range of cation exchange capacity values.