Image: A huge pilar in Postojnska Jama, Slovenia.

speleothem: A secondary mineral deposited in a cave by the action of water. Also known as cave formation.
From: Sybil P. Parker ed. (1997): McGraw-Hill Dictionary of Geology and Mineralogy, 380 pages, McGraw-Hill; ISBN: 0070524327  amazon.com

The most common speleothems consist of calcite (CaCO3), aragonite (CaCO3) or gypsum (CaSO4). Some common types are:

 Boxwork Thin plates of calcite forming boxes.
 Cave Coral Very small short stalks with bulbous ends, usually occurring in numbers in patches.
 Cave Pearl A smooth, polished and rounded speleothem found in shallow hollows into which water drips.
 Column, Pillar A speleothem from floor to ceiling, formed by the growth of a Stalactite and a stalagmite to join, or by the growth of either to meet bedrock.
 Curtain, Shawl, Bacon Rind A speleothem in the form of a wavy or folded sheet hanging from the roof or wall of a cave, often translucent and resonant.
 Diadochite speleothems looking like stalactites and stalagmite, found in mines, growing extremely fast.
 Dogtooth Spar huge calcite cristals forming crusts on floor and walls, formed in standing water.
 Helictite, Eccentric A speleothem of abnormal shape or attitude.
 Moonmilk, Rockmilk A soft, white plastic mineral consisting of Calcite, hydrocalcite, hydromagnesite or huntite.
 Pillar A dripstone where the stalactite- and stalagmite-part are grown together.
 Rimstone Pool Pools with very thin calcite rims.
 Shield a calcite conretion in the form of a thin disc, a circuar plate forming at the wall.
 Stalactite A dripstone hanging downwards from a roof or wall, of cylindrical or conical form, usually with a central hollow tube.
 Stalagmite A dripstone projecting vertically upwards from a cave floor and formed by precipitation from drips.
 Straw (-stalactite) A long, thin-walled tubular Stalactite less than about 1cm in diameter.

See also

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