SUMMARY The underlying Cole-Cole model of the frequency dependence of complex conductivity and resistivity predicts two time constants that are not identical but which are related to each other. The shorter time constant [Formula: see text] predicts the current response to a voltage step and, in various models of a mineralized grain, is related to the intrinsic properties of the polarizable component, whereas the longer time constant [Formula: see text], which predicts the voltage response to a current step, is dependent on intrinsic material properties and also the relative volume of polarizable material as defined through chargeability. As a consequence, although we agree with most of the conclusions of the original paper, the specification [Formula: see text] instead of [Formula: see text] in reference tables will simplify.