Crystals slide past one another without changing crystal shape. Ideally, the grain fabric and texture of the deformed product will look just like that of the starting material. The movement of one grain past another, in pure material may be accomplished by dislocation or diffusive mechanisms. The shape of any object will be an influence on its mechanical behaviour, elongate grains will be more prone to buckling than spherical ones, and if a series of elongate grains are all aligned, it makes it easier for them to deform by grain boundary sliding. Similarly elongate grains will have a mechanical coupling on them that will tend to rotate them with respect to the applied stress that spherical grains will not have. Grain boundary orientations allow easier grain boundary sliding, Grain neighbour switch requires the grain boundary sliding. In case of rocks which are consolidated or compacted by tectonic deformation, this process plays an important role in the initial deformational stages. Since Nabarro Herring Creep and Coble Creep are essentially involved in deformation close to or athe grain boundaries, these are two dominant mechanisms that operate in conjunction with grain boundary sliding.

Jessel at al Monash Au