Under conditions of slow evaporation of salt solutions imbibed in a porous, fine-grained stone, polycrystalline whiskers are observed to develop at pores and channels in the surface. SEM examination of these growths shows that they develop by being extruded outward from the mouth of the pore; consequentlym they detach material, such as paint film, that may be deposited on the surface. In the solution-mediated transformation of single-crystal calcite into a pseudomorphic polycrystalline mass of fluorite, SEM examination shows that the initial stage is the precipitation of charged colloidal particles, which subsequently undergo diffusion-controlled recrystallization into idiomorphic fluorite with a morphology dictated by the micration paths of the solute ions.