Caves are natural spaces created by weathering of rocks. Of the many caves, the most common type is the limestone cave. Over millions of years, acidic groundwater or underground rivers dissolve away the limestone, leaving cavities which grow over time. Structures inside a cave may require millions of years to develop. Of the many structures, stalagmites and stalactites are two beautiful phenomena.
Limestone caves are composed of calcite (calcium carbonate), a common mineral in sedimentary rocks. When it rains, water combines with minerals from limestone and carbon dioxide. This results in the formation of calcium bicarbonate. It combines with air inside the caves to form calcium carbonate. Water carries this substance through the cracks of the roofs. The caves slowly get adorned with calcium carbonate formations produced through slow precipitation. These secondary mineral deposits in caves are called speleothems.
Both stalactites and stalagmites in greek means ‘to drip’. Dripping is how they get formed. They grow as water drips from the roofs of limestone caves. Water reacts with carbon dioxide and forms carbonic acid. It then seeps slowly through the roof of the cave depositing calcium carbonate which hardens and builds up over time to form a stalactite.
Stalagmites too form exactly the same way but on the floor of caves rather than from the roof. They rise from the floor in a buildup of calcium carbonate over time from the mineral bearing water that drops from the roof of the cave.