What rock is dissolved by acidic groundwater forming caves?

What rock is dissolved by acidic groundwater forming caves?

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

Answer: (A)

This question tests how caves form through chemical weathering when acidic groundwater dissolves soluble rocks. Limestone is mainly calcium carbonate, which readily reacts with carbonic acid in water produced from dissolved CO2. The dissolved rock turns into ions, Ca2+ and HCO3-, effectively dissolving the rock and enlarging openings over time. The key reaction is CaCO3 + CO2 + H2O → Ca2+ + 2HCO3-. As these cavities grow, they become caves. Other rocks like granite, sandstone, and shale aren’t dissolved as easily by natural groundwater. Granite’s minerals (quartz and feldspar) and the cementing minerals in sandstone and shale are much less soluble, so they’re more likely to weather by physical breakdown or slower chemical processes rather than forming extensive dissolution caves. That’s why limestone regions commonly develop karst landscapes with caves.

This question tests how caves form through chemical weathering when acidic groundwater dissolves soluble rocks. Limestone is mainly calcium carbonate, which readily reacts with carbonic acid in water produced from dissolved CO2. The dissolved rock turns into ions, Ca2+ and HCO3-, effectively dissolving the rock and enlarging openings over time. The key reaction is CaCO3 + CO2 + H2O → Ca2+ + 2HCO3-. As these cavities grow, they become caves.

Other rocks like granite, sandstone, and shale aren’t dissolved as easily by natural groundwater. Granite’s minerals (quartz and feldspar) and the cementing minerals in sandstone and shale are much less soluble, so they’re more likely to weather by physical breakdown or slower chemical processes rather than forming extensive dissolution caves. That’s why limestone regions commonly develop karst landscapes with caves.