Which one of the following is NOT considered as a chemical weathering?

Correct option is D

The correct answer is (D) Calcification

Explanation:
• Chemical weathering refers to the decomposition of rocks through chemical reactions that change the mineral composition.
• Hydrolysis: The chemical breakdown of a substance due to reaction with water; it is a primary process in the weathering of feldspars to clay.
• Carbonation: The reaction of carbonic acid (from $CO_{2}$ and water) with minerals like limestone.
• Reduction: Occurs in environments lacking oxygen (like waterlogged soils), changing the oxidation state of minerals like Iron ($Fe^{3+}$ to $Fe^{2+}$).
• Calcification: This is a soil-forming process (Pedogenic process), not a weathering process of primary rocks. It involves the accumulation of calcium carbonate in the soil profile, typically in arid or semi-arid regions.

Information Booster:
• Other chemical weathering processes include Hydration (absorption of water) and Oxidation (reaction with oxygen).
• Weathering is the 'input' or preparatory stage for soil formation, whereas processes like calcification happen within the developed soil body.

Additional Knowledge:
• Hydrolysis (Option A): Considered the most important chemical weathering process for silicate minerals.
• Carbonation (Option B): Highly responsible for the formation of Karst topography (caves and sinkholes).
• Reduction (Option C): Leads to the development of 'gleying' or mottled colors in subsoil.