When a rock is subjected to nonhydrostatic stress, some grain boundaries will be under deviatoric compression and others will be under deviatoric tension. This small change in stress causes a change in Gibbs free energy that can drive dissolution of minerals (typically in response to compression) and their reprecipitation in veins or along grain boundaries (typically in response to tension). Oolites are plastically deformed as well as underwent large pressure solution giving rise to tectonic stylolites.

Plastic flow takes place by deformation of the crystal lattice of individual minerals without fracture or granulation. It occurs by the movement of crystal defects (errors) within the crystal structure. Three basic types of defects are: (search in this dictionary ) (i) Point defects (vacancies or impurity atoms), (ii) Line defects (dislocations) and (iii) Planar defects (stacking faults).

Line defects are particularly important for deformation in rocks by mechanisms of dislocation glide and twin glide. see dislocations and dislocation glides.