Electron irradiation of CaF2with 2 keV electrons causes metallization of the surface and near surface layers by the formation of colloids. Colloids on the surface are significantly larger than those in the bulk indicating a higher mobility of defects on the surface. Optical spectroscopy on extinction bands of bulk colloids reveals Ostwald ripening as the driving force for aggregation, while scanning force microscopy results suggest that similar processes dominate the early stages of surface colloid formation.