THE CHEMISTRY OF LIMESTONE STALACTITES

Stalactites and stalagmites form when rainwater drips through limestone rock. Along the way, it picks up carbon dioxide from the air and from any organic matter it passes as it dribbles down. The carbon dioxide reacts with the water to make a weak acid called carbonic acid. This acid can dissolve limestone, reacting with the mineral calcite and drawing it into the water as calcium bicarbonate. As water drips into a cave, it comes into contact with air again. It then lets go of the carbon dioxide and the calcium comes out of the solution, forming rock-hard calcite again.