stalactite and stalagmite at English => English (The Britannica Concise) Of Explained:
Elongated forms of various minerals deposited from solution by slowly dripping water. A stalactite hangs like an icicle from the ceiling or side of a cavern. A stalagmite rises from the floor of a cavern. The two are not necessarily paired; when they are, continual elongation of one or both may eventually join them into a column. The dominant mineral in such deposits is calcite (calcium carbonate), and the largest displays are formed in caves of limestone and dolomite.