Ion‐bombardment‐induced compaction of fused silica is measured using a cantilever plate technique for H, He, O, Ne, and A ions with a variety of ion energies. A phenomenological theory is developed which is based on the superposition of two independent compaction mechanisms, one proportional to the density of energy deposited into atomic collisions and the other dependent on the density of energy deposited into electronic excitations. All the present experimental data can be fit to within experimental error with the model using only three adjustable parameters and ion‐energy partitioning calculations. Further substantiation of the present energy partitioning calculations and model are provided by showing the proportionality between the density of energy deposited into atomic collisions and other workers' published results for ion‐bombardment‐induced index‐of‐refraction changes in quartz and fused silica. It is concluded that the atomic‐collision‐induced‐compaction and index‐of‐refraction changes are ion independent. Finally, a dose‐rate dependence of the ionization‐induced compaction is noted for the first time.