Which one of the following processes of weathering belongs to both mechanical and chemical weathering ?

Hydration is a chemical weathering process involving the rigid attachment of H+ and OH- ions to a mineral's molecules, leading to chemical alteration [c2, t1]. However, it also functions as a mechanical process because the absorption of water causes minerals to expand in volume, creating significant physical stress within the rock [c2]. For instance, the conversion of iron oxides to iron hydroxides increases volume, leading to physical disintegration through fatigue, exfoliation, and granular disintegration [c2]. While crystallization (salt weathering) is primarily mechanical due to crystal growth pressure [c1, t4], and carbonation is strictly chemical [t3, t9], hydration uniquely bridges both categories by using chemical bonding to trigger mechanical expansion and structural failure [c2, t6]. Water acts as the central agent in this dual-action process, facilitating both the chemical change and the resulting physical alteration [t6].

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Hydration > p. 91
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 6: Geomorphic Movements > Salt Weathering > p. 85