Stalactite

A stalactite is an underground feature found in limestone areas. They form in an underground cave. Stalactites can be found in Ailwee Caves in the Burren.
Limestone is a permeable rock meaning that water can pass through it. Water can flow through vertical cracks in the rock. Water can then flow along the bedding planes, which are horizontal gaps between different layers or rock. It is because of limestone permeable characteristics that carbonation can occur. Carbonation is a form of chemical weathering. Carbonic acids forms from carbon dioxide and rainwater. This dissolves calcites in the limestone, which becomes calcium bicarbonate.

Stalactites form on the roof of underground caverns. Water seeps through joints in the rock until it reaches the roof of a cave. This water contains calcium bicarbonate. In the caves, some of the water will evaporate, leaving traces of calcium bicarbonate on the roof. This will solidify to become calcite again. Each drop leaves calcite on the ceiling of the cave. The deposited calcite is called dripstone. Most of the calcite is deposited at the circumference of the water drops, which explains why stalactites are generally so thin. The stalactite continues to grow because of a constant supply of water and calcium bicarbonate from the overhead joint.

The calcite grows downwards due to gravity. The rate of growth is estimated to be approximately 7mm per year.