The nature of grain boundaries is very important, since fluids here actually come in contact with all grains. As islands and channels constantly migrate, the fluid can access the whole grain surface over time. Dissolution precipitation creep Dissolution-precipitation creep is a deformation mechanism that involves three serial steps. The slowest of these three steps is the rate controlling step. Provided there is a suitable fluid, it may also be important at higher temperatures.
Grain boundaries have to transmit stresses from grain to grain.
Diffusions is rate controlling The whole of Dm is used to drive the diffusion, if precipitation and dissolution are relatively fast. Pressure solution creep is favoured by a small grain size, and the grain size must be especially small for reaction controlled pressure solution creep. As a deformation mechanism, long distance transport is not very important, but it is as a significant process that produces structures in rocks, such as veins, stylolites and cleavages. In other words a heterogeneous distribution of precipitation and dissolution. Stylolites are often oriented normal to the maximum compression direction.