This simulation shows one inclined slip plane with loops being generated continuously. Twinning Unlike dislocation glide, movement of a twin boundary significantly and permanently alters the orientation of the crystal. The orientation of the twin plane, and the misorientation across the twin boundary will be precisely the same for any particular type of twin, and the process of twinning is essentially instantaneous, there is not a gradual change in crystallographic orientation, as the twin boundary moves across a region, the crystal lattice flips, and a discrete increment of deformation is attained. They are particularly important in the low temperature deformation of calcite, and the deformation of plagioclase. Here is a movie of twin development in bischovite, a hydrated magnesium salt, made by Janos Urai.
Micas often deform by kinking, which involves slip on the basal plane.
Grain boundary sliding The movement of one grain past another, in pure material this may be accomplished by dislocation or diffusive mechanisms. Light gray atoms are in local hexagonal close packing order, which for example corresponds to stacking faults. Similarly a feldspar lath in a granite melt can rotate with essentially no internal deformation if the melt is sheared. See lecture 5. They are contoured in strain rates, showing the strain rate that would be achieved by that process alone under the appropriate conditions.