In this paper we report a study of the coercivity of Fe-SiO2 granular solids, with Fe volume concentrations between 0.2 and 0.6, and mean grain sizes varying from 15 to 18nm. These samples present very high switching fields of the order of 1kOe, being higher for the magnetization processes than for the demagnetization ones. The analysis of the switching field distributions and the calculation of the activation volumes have proved that the reversal mechanism is the same for all samples, either above or below the percolation threshold (x=0.5), and involves the full volume of individual particles, aided by dipolar fields that are of a few hundred Oe, in the case of the demagnetization processes.