Methods and apparatus for evaluating a volume of an earth formation wherein the volume comprises a fluid-saturated rock matrix including clay particles. Methods include making measurements of complex permittivity at a plurality of frequencies using an electromagnetic tool in a borehole penetrating the earth formation; and estimating a plurality of parameters of interest simultaneously using the measurements at the plurality of frequencies and a mixing model accounting for electrical effects on the measurements caused by the clay particles. The plurality may include at least: i) water saturation; and ii) resistivity of formation water. Parameters of interest may comprise at least one of: i) an electrical parameter of the volume; and ii) a textural parameter of the volume. Methods may include modeling for electrical effects caused by at least one of: i) a surface conductivity of the clay particles; and ii) a textural property of the clay particles.