Forming Stalagmites

Stalagmites form when limestone is deposited in a precipitation reaction.

The water running into limestone caves is often acidic. This can occur if it has absorbed carbon dioxide that has been given off by rotting material in the soil. As the acidic water runs through openings in the limestone (calcium carbonate) it breaks the bonds holding the calcium and the carbonate together and dissolves.

As the water and limestone solution runs through the cave carbon dioxide is lost into the air. The water is no longer acidic so the bonds between the calcium and the carbonate can reform giving solid limestone. The limestone is deposited and a stalagmite, stalagtite or column gradually builds up.