Agents of chemical weathering in soils: Which of the following processes contribute to chemical weathering of parent rock and soils?

Introduction / Context:Chemical weathering alters mineralogy and fabric of soils, impacting plasticity, strength, and durability. Recognizing the key chemical processes helps interpret soil genesis and anticipate engineering behavior such as susceptibility to collapse or swelling.

Given Data / Assumptions:

• Parent rock contains minerals susceptible to oxidation, hydration, and dissolution.
• Water and gases like oxygen and carbon dioxide are present.

Concept / Approach:Oxidation converts ferrous to ferric iron, generating oxides/hydroxides (reddening). Carbonation forms carbonic acid that attacks carbonates and feldspars. Hydration adds water to mineral structures (e.g., anhydrite to gypsum). Leaching dissolves and carries away soluble constituents, altering soil chemistry and structure.

Step-by-Step Solution:

Verification / Alternative check:Field soil horizons (e.g., B-horizon accumulations) and laboratory mineralogical tests show products of these reactions.

Why Other Options Are Wrong:

• Limiting to one process ignores the multi-mechanism nature of chemical weathering.

Common Pitfalls:Confusing chemical with mechanical weathering (freeze–thaw, abrasion); underestimating climatic control (temperature, rainfall).

Final Answer:All of the above