stalactites and stalagmites
Rainwater percolates through the rocks above the cave and, as it contains atmospheric carbon dioxide, can dissolve calcium carbonate en route. On reaching the cave, the water drips from the roof to the floor; as a drop hangs, some water evaporates, leaving a little calcium carbonate as calcite on the roof. Repetition forms a stalactite; and evaporation of the fallen water on the floor forms a stalagmite.
On occasion, the rising stalagmite and descending stalactite fuse to form a column. Stalactites, stalagmites, and columns are called dripstone because they are deposited by dripping water.
Related category GEOLOGY AND PLANETARY SCIENCE
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