Rock oxidation

What is Chemical Weathering?

Chemical reactions in general happen when something is out of equilibrium with its surrounding environment. Chemical weathering is the process where rocks and minerals, which originally formed deep underground at much higher temperatures and pressures, gradually transform into different chemical compounds once they are exposed to air and water at the surface. The farther out of equilibrium a particular mineral is, the faster it will weather. In general, the new chemical forms are structurally weaker than the original rock, which causes the rock to eventually disintegrate.

Types of Chemical Weathering

There are three basic types of chemical reactions that cause four types of chemical weathering of rocks. Dissolution and hydrolysis are caused by reactions with acids. Hydration is the absorption of water. Oxidation is reaction with oxygen.

1. Acid Reactions

Acids are chemical compounds that produce H+ ions when dissolved in water. The stronger the acid, the more H+ ions they produce. Acids can react with any rock mineral that has other positive ions, like Ca++, Na+, or K+, by taking their place - which changes the chemical composition of the mineral and disrupts its atomic structure.

The most important natural acid is carbonic acid (H2CO3), which forms from carbon dioxide and water (CO2 and H2O). Others include sulfuric acid (H2SO4) and hydrofluoric acid (HF) which mainly come from volcanic eruptions.