ABSTRACT
Thus, a mineral (part of a rock) that formed and was at equilibrium under conditions of elevated temperature and pressure is unstable at earth surface conditions. The acidic water, possibly aided by temperature fluctuations, attacks the mineral and a series of chemical reactions ensue producing a series of new minerals which are at equilibrium under the new conditions. If there is sufficient time, then ultimately the end of the search for thermodynamic equilibrium produces clay minerals with lesser quantities of other colloidal materials. This is the process known as weathering and is the major source of sediments and soils at the earth's surface on the continents and blanketing
much of the oceans. Since the clay minerals form at low temperatures (in a geological sense), reaction rates are slow and crystals of these new phases form slowly and imperfectly resulting in very small particle sizes, far smaller than would result from mechanical abrasion of larger crystals.
