Chemical Weathering Processes on the Earth’s Surface

Abstract

The exhumation of rocks from the Earth’s crust implies that they must adjust thermodynamically to the conditions existing on the surface, which are extremely different from those prevailing during their formation, with higher temperature, pressure, and often exposed to chemically aggressive fluids. The processes involved in chemical weathering, such as dissolution, hydrolysis, etc., are at the core of the adjustment mechanism, transforming solid, and usually refractory rock material, into particles-typically stripped from part of their original components and dissolved phases, both of which are amenable to be transported from the continents to the sea. Although anthropogenic actions have altered natural denudation rates, still a relatively minor portion of the material thus produced stays for a longer period on the continents, temporarily sequestered in depositional systems. The most important participants in the weathering scenario are mineral dissolution, silicate hydrolysis, and redox reactions.

Glossary

Cation exchange capacity

: Is the maximum quantity of total cations that a soil or sediment is capable of holding, and is available for exchange with the soil solution at a given pH value.

Cenote

Is a deep natural pit, or sinkhole, characteristic of Yucatán (Mexico) that results from the collapse of limestone, exposing the groundwater underneath.

Congruent dissolution:

Weathering reaction between a mineral and water that results in its complete dissolution.

Diagenetic processes:

Are changes that occur in sediment or sedimentary rocks during and after rock formation (lithification), at temperatures and pressures less than that required for the formation of metamorphic rocks or melting.

Hydrate:

A substance that contains water of crystallization or water of hydration, in a definite ratio as an integral part of the crystal.

Incongruent dissolution:

Weathering reaction between a mineral and water that results in its partial dissolution and a solid residue.

Karst:

Is a geological formation shaped by the dissolution of soluble bedrock, usually carbonate rock but also in gypsum. Given the right conditions it can also occur in weathering-resistant rocks, such as quartzite.

Monomer:

Is a molecule that may bind chemically to other molecules to form a polymer.

Playa:

Is an ephemeral lakebed, or a remnant of an endorheic lake, consisting of fine-grained sediments infused with alkali salts. Alternative names include dry lake or alkali flat.

Regolith:

I Layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons

Solubility product:

Is a constant (K_sp) for a solid substance dissolving in an aqueous solution; represents the level at which a solute dissolves in solution.