The mechanical, chemical, or biological action of the atmosphere, hydrometeors, and suspended impurities on the form, color, or constitution of exposed material; to be distinguished from erosion. Mechanical weathering results from the disintegrating action of high or low temperature, large changes of temperature, frost, or the impact of wind-borne sand or water (e. G. , frost action, scouring, etc. ). Chemical weathering is due to the chemical action of atmospheric constituents, especially acid impurities, in a moist atmosphere or in rainwater (e.g. Corrosion, oxidation, etc. ). Biological agents are mainly fungi that attack organic material (e. G. , rotting, mildew, etc. ).