Which one of the following processes leads to expansion of certain minerals as they take up water, causing additional stress in the rock?

Hydration is a chemical weathering process involving the addition of water to a mineral's structure through the attachment of H+ and OH- ions [1]. This process leads to a significant increase in the volume of the minerals, which creates physical stresses within the rock [1]. For instance, the reaction of anhydrite with water transforms it into gypsum, a mineral with a larger volume. Similarly, iron oxides convert to iron hydroxides, which are larger and exert pressure on the surrounding rock structure [1]. This repeated expansion and contraction (as hydration is often reversible) causes fatigue, eventually leading to rock disintegration through mechanisms like exfoliation and granular disintegration [1]. While hydrolysis involves the chemical breakdown of minerals into new substances like clay, hydration specifically emphasizes the swelling and physical stress caused by water absorption [1].

Sources

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