The expansion exerts a force on the sizes of the crack which may cause the crack to widen. Repeated freezing and thawing can reduce a large exposure to millions of individual particles. In mountainous regions these particles may accumulate at the bottom of steep slopes forming talus piles When erosion exposes an igneous body at the surface the pressure acting on the rock is reduced considerably. These exfoliation domes are quite common. The loose material released by physical weathering is termed sediment .
Oxidation involves the loss of electrons.
Recall that oxygen has an affinity for two electrons which will result in a filled s and p set of orbitals. This gives the oxygen anion a net negative charge of -2. Some of its valence electrons can be removed by an oxidizing agent. Another common pigmentation agent is organic matter which produces a black color. Oxidation is enhanced when sediment is close to the atmosphere.