Statement 1: Rocks undergo both physical and chemical changes. This statement is correct. Rocks are constantly affected by processes that break them down and alter their composition. These processes are broadly categorized into physical (mechanical) weathering and chemical weathering.
Physical Weathering: This involves the disintegration of rocks without any change in their chemical composition. Examples include frost wedging, thermal expansion and contraction, abrasion, and the action of plant roots.
Chemical Weathering: This involves the decomposition of rocks through chemical reactions, leading to a change in their mineral makeup. Examples include dissolution (e.g., limestone dissolving in acidic water), oxidation (rusting of iron-bearing minerals), and hydrolysis (reaction with water).
Statement 2: Physical weathering involves a change in the rock's mineral makeup. This statement is incorrect. As stated above, physical weathering breaks rocks into smaller pieces but does not alter the chemical or mineralogical composition of the rock itself. Chemical weathering is responsible for changes in mineral makeup.
Statement 3: Cracking and expansion are signs of weathering. This statement is correct. Cracking and expansion are direct consequences of weathering processes. For instance, frost wedging causes water to seep into cracks, freeze, expand, and widen the cracks. Thermal expansion and contraction due to temperature fluctuations can also lead to cracking. These are key indicators of physical weathering in action.
