text: Dislocation creep is a non-linear (plastic) deformation mechanism in which vacancies in the crystal glide and climb past obstruction sites within the crystal lattice. These migrations within the crystal lattice can occur in one or more directions and are triggered by the effects of increased differential stress. It occurs at lower temperatures relative to diffusion creep. The mechanical process presented in dislocation creep is called slip. The principal direction in which dislocation takes place are defined by  a combination of slip planes and weak crystallographic orientations resulting from vacancies and imperfections in the atomic structure. Each dislocation causes a part of the crystal to shift by one lattice point along the slip plane, relative to the rest of the crystal. Each crystalline material has different distances between atoms or ions in the crystal lattice, resulting in different lengths of displacement. The vector that characterizes the length and orientation of the displacement is called the Burgers vector. The development of strong lattice preferred orientation can be interpreted as evidence for dislocation creep as dislocations move only in specific lattice planes.
  Dislocation glide cannot act on its own to produce large strains due to the effects of strain-hardening, where a dislocation ‘tangle’ can inhibit the movement of other dislocations, which then pile up behind the blocked ones causing the crystal to become difficult to deform. Diffusion and dislocation creep can occur simultaneously. The effective viscosity of a stressed material under given conditions of temperature, pressure, and strain rate will be determined by the mechanism that delivers the smallest viscosity. Some form of recovery process, such as dislocation climb or grain-boundary migration must also be active. Slipping of the dislocation results in a more stable state for the crystal as the pre-existing imperfection is removed. It requires much lower differential stress than that required for brittle fracturing. This mechanism does not damage the mineral or reduce the internal strength of crystals.