The vast majority of sorption data used in performance assessment studies for radioactive waste repository concepts has been generated from small-scale laboratory batch sorption measurements on crushed rock samples. Since these data will mainly be used to describe the sorption on the in situ bulk rocks in safety studies, a justifiable and defensible procedure for making the transfer of sorption values from the laboratory data to data appropriate to the field conditions is required. At the present time, a generally accepted methodology for doing this is lacking, and little or no work is being carried out internationally on this important area. The question of whether the act of crushing is intrinsically likely to lead to higher sorption values than for intact rock because the area available for sorption has been increased is addressed here. The approach is based on comparing N2-BET surface area measurements on intact and crushed single minerals and rocks. Results are presented which indicate that the clay mineral content of the rock is critically important in this respect, whereas the influence of the rock porosity is only of minor consequence.