Stalactite
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Water droplet coming out of the central canal of a stalactite |
A
stalactite (
Greek stalaktos, (Σταλακτίτης), "dripping" or "dropped"), or
dripstone, is a type of
speleothem that hangs from the ceiling or wall of
limestone caves.
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Stalactites from a cave in Yucatán. |
Stalactites are formed from the deposition of
calcium carbonate and other minerals, which is precipitated from mineralized water
solutions. The corresponding formation on the floor underneath a stalactite is known as a
stalagmite. Given enough time, these formations can meet, resulting in a formation known as a column or pillar.
Every stalactite begins with a single mineral-laden drop of water. When the drop falls, it leaves behind the thinnest ring of calcite. Each subsequent drop that forms and falls deposits another calcite ring. Eventually, these rings form a very narrow (0.5 mm), hollow tube commonly known as a "soda straw" stalactite. Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.
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Mineralized water drop forming at bottom of stalactites. |
The same water drops that fall from the tip of a stalactite deposit more calcite on the floor below, eventually resulting in a rounded or cone-shaped stalagmite. Unlike stalactites, stalagmites never start out as hollow "soda straws."
The longest stalactite known hangs in the Chamber of Rarities in the
Gruta Rei do Mato (
Sete Lagoas,
Minas Gerais,
Brazil). It is 20 metres long.
Stalactites and stalagmites can also form on concrete ceilings and floors, although they form much more quickly there than in the natural cave environment.
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Icicle*
Rusticle*
Karst*
Ice spike*
The Virtual Cave's page on stalactites
