Helium or proton beams, penetrating several microns or more, cause crazing on vitreous silica surfaces. In a lower energy range (beams up to 150 keV were used) there was observed upon irradiation a plastic flow stress relaxation that relieved the stress from the radiation‐induced dilatation and resulted in the total volume change in vitreous silica or quartz occurring perpendicular to the surface! Implications of this radiation‐induced stress relaxation seem fundamental to the radiation behavior of quartz, silica, and similar substances, and are discussed.