The weathering process breaks down rocks.
Weathering is the set of processes whereby rocks and minerals on Earth’s surface are broken down over time. Chemical weathering involves the chemical alteration of these rocks and minerals. One type of chemical weathering is oxidation.
Oxidation reactions involve a increase in oxidation state–in other words, the transfer of electrons from a compound that is oxidized to the compound that oxidizes it. Oxygen gas is a major component of Earth’s atmosphere and is fairly reactive–so much so, in fact, that it’s good at combining with metals and compounds in minerals, oxidizing or “rusting” them.
When oxygen in the atmosphere oxidizes iron-bearing compounds in minerals, the intermolecular forces between the molecules of the resulting iron oxides are weaker. The rusted or oxidized mineral crumbles more easily, in the same way that rust crumbles more readily than solid iron, and erodes more readily.
Minerals that may become oxidized through contact with oxygen in Earth’s atmosphere include olivine, pyroxene, amphibole and biotite. Iron oxides formed by oxidation of iron in these minerals are reddish-orange or brown in color.