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: