(Boulder set on ocean side rocks by Mother Nature at Sandford,NS)
I've always loved stones. As a child I spent much of my spare time wondering the fields looking at the stone walls and boulders left by those people before me who cleared the rough stony Nova Scotia soil to make it there home. Weathering of stones are fascinating also. With icy storms, wind swept beaches and fields and the rocks of Metamorphic Rocks/ Sedimentary Rocks its a natural art exhibition!
Erosion is the main physical agent responsible for stone weathering. Particular emphasis is placed on the effects of wind and water. Erosion occurs in windy regions with sandy terrain, but in urban areas it is extremely rare and is often confused with other forms of deterioration. The problem of condensation on surfaces and in pores is extensively discussed, in relation to pore shape and size. Physical effects dominate in the smallest pores, and solution effects in the largest ones. Small veins in the stone rise, increase because of pressure , freezing-thawing cycles and micro meteorological conditions favorable for the soaking of monuments are discussed. A final section is devoted to the dissolution of stones and the formation of black crusts as a consequence of the way the stone is washed out or simply wet by water. The intensity of rainfall is important in activating or removing the dry pollutant deposits that form on monuments, especially during the dry periods characteristic of the Mediterranean climate. Condensation plays a minor role compared with rainwater. However, the porosity, geometrical shape and exposition of the stone are also important factors which can characterize different local balances and, consequently, the form of weathering.
(most of this info stolen from Physical weathering of stones)