'Chemical Weathering' can be defined as the dissolution of minerals by the action of water and its solutes. It is an important feature of the global hydrogeochemical cycle of elements, whereby rocks and primary minerals become transformed to solutes and soils and, eventually, to sediments and sedimentary rocks. In the cycle, water occupies a central position serving as both a reactant and a transporting agent of suspended and dissolved material. The sea is the ultimate receptacle of weathered material, and the atmosphere provides a reservoir of weak acids (CO2) and oxidants. A comparison of laboratory weathering rates and estimates from the field indicated that laboratory rates were one to two orders of magnitude greater than field estimates of chemical weathering. The discrepancy is likely due to the difficulty of estimating a suitable wetted surface area of weatherable (reacting) minerals in the field, and the possibility of hydrologic control, due to micropore flow through soils.