Paper 1 · June 2004 · Slope Processes and Weathering
Granite is an impermeable, crystalline igneous rock, while limestone is a permeable sedimentary rock composed largely of calcium carbonate. Why is limestone especially susceptible to chemical weathering?
AIts dark surface colour absorbs extra solar radiation, accelerating thermal expansion cracking
BIts high iron content oxidises rapidly whenever it is exposed to moist air
CIts crystalline structure expands and contracts sharply with the daily temperature changes typical of granite
DCalcium carbonate in limestone dissolves readily in slightly acidic rainwater through carbonation
Explanation
Limestone's calcium carbonate reacts with the weak carbonic acid formed when rainwater absorbs atmospheric carbon dioxide, dissolving the rock through carbonation; the other listed processes describe weathering of other rock types, not limestone's particular chemical vulnerability.
Derived from ZIMSEC Geography Paper 1, June 2004, Q6