Mineral Weathering and Soil Formation

Mineral weathering and soil formation describe the chemical breakdown of rock-forming minerals and the genesis of soils, releasing elements and producing the secondary minerals that dominate soil reactivity.

Definition

The chemical processes by which minerals dissolve and transform during weathering and contribute to the formation and evolution of soils.

Scope

This topic covers the dissolution and transformation of primary minerals by water, acids, and biological activity, the formation of secondary clays and oxides, and the chemical aspects of soil development. It connects weathering to nutrient supply, alkalinity generation, and long-term carbon dioxide regulation.

Core questions

• What reactions drive the chemical weathering of minerals?
• Which secondary minerals form during soil development?
• How does weathering supply nutrients and consume carbon dioxide?
• What controls weathering rates in the field?

Key theories

Hydrolysis and acid-promoted weathering

Silicate and other primary minerals weather chiefly by hydrolysis and proton- and ligand-promoted dissolution, releasing base cations and silica and forming clays and oxides that govern soil chemistry.

Mechanisms

Carbonic and organic acids and water attack mineral surfaces, breaking bonds and releasing ions; the products reprecipitate as secondary clays and iron and aluminum oxides. The consumption of protons during silicate weathering generates alkalinity, linking weathering to the long-term carbon cycle.

Clinical relevance

Weathering supplies nutrients, builds the reactive secondary minerals that retain contaminants, and provides a natural buffer against acidification, while also drawing down atmospheric carbon dioxide over geological time.

History

Geochemical understanding of weathering matured with Goldschmidt's element-distribution work and 20th-century studies of mineral dissolution kinetics and soil genesis.

Key figures

• Victor Goldschmidt

Seminal works

• sposito2008
• vanLoon2017

Frequently asked questions

How does rock weathering affect the climate?

Silicate weathering consumes carbon dioxide as carbonic acid, acting over geological timescales as a slow regulator of atmospheric carbon dioxide.