Weathering refers to the processes by which rocky material is subjected to physical disintegration and chemical decomposition when exposed to atmospheric or hydrospheric agents near the surface of the Earth. During weathering, rocks change color, texture, chemical and mineralogical composition, firmness, and/or form, with little or no transport of the loosened or altered material. The action of water and oxidizing conditions destabilizes high-temperature minerals such as olivine, pyroxene, or plagioclase, converting them to low-temperature secondary minerals, mainly clays and iron oxides. In this process, the rock is converted partially or completely from hard solid material, commonly with large interlocking crystals, to soft, unconsolidated, hydrous, fine-grained material that is then subject to mechanical erosion.
Two types of weathering can be distinguished: Mechanical weathering involves breakdown of the mineral or rock structure by the physical...