Which rock does dissolution by acidic groundwater form caves?

Which rock does dissolution by acidic groundwater form caves?

• A. Granite
• B. Sandstone
• C. Limestone
• D. Shale

Answer: (C)

Dissolution by acidic groundwater mainly forms caves in rocks that are made of a mineral that readily dissolves in weak acids. Limestone is rich in calcium carbonate (CaCO3), so when rainwater absorbs CO2 and becomes carbonic acid, it reacts with the calcite in limestone and dissolves it. As this acidic water percolates through cracks and joints, it slowly enlarges openings to create caves. The basic chemical reaction is CaCO3 + H2CO3 → Ca2+ + 2 HCO3−, showing how calcium carbonate is removed by the acidified water. Other rocks like granite (which is mostly silicates), sandstone, and shale don’t dissolve as easily in weak acids, so they don’t form large caves by dissolution in the same way limestone does. This is why limestone landscapes often display cave systems and karst features.

Dissolution by acidic groundwater mainly forms caves in rocks that are made of a mineral that readily dissolves in weak acids. Limestone is rich in calcium carbonate (CaCO3), so when rainwater absorbs CO2 and becomes carbonic acid, it reacts with the calcite in limestone and dissolves it. As this acidic water percolates through cracks and joints, it slowly enlarges openings to create caves. The basic chemical reaction is CaCO3 + H2CO3 → Ca2+ + 2 HCO3−, showing how calcium carbonate is removed by the acidified water. Other rocks like granite (which is mostly silicates), sandstone, and shale don’t dissolve as easily in weak acids, so they don’t form large caves by dissolution in the same way limestone does. This is why limestone landscapes often display cave systems and karst features.