Stalactites

These are the formations everyone thinks of when they think of caves. Water seeps through from above and forms a droplet that hangs from the roof. Carbon dioxide is released fromt he water into the surrounding atmosphere. The water may evaporate slightly as well. This has the effect of causing the dissolved calcium carbonate to forms crystals of calcite that are attahced to the ceiling of the cave.

Initially when a stalactite forms it is like a drinking straw. The crystal has formed around the edge of the drop of water and continues to do so, forminga tube that hangs down. Eventually the tube becomes blocked which forces the water to be exuded through the walls of the stalactite and to run down the outside. When this happens the stalactite starts to become thicker as well as longer.