Speleothem

A speleothem (pronunciation: /ˈspiːliːəθɛm/; Ancient Greek: "cave deposit"), commonly known as a cave formation, is a secondary mineral deposit formed in a cave. Speleothems typically form in limestone or dolostone solutional caves. The term "speleothem" as first introduced by Moore (1952), is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem" in most publications, specifically excludes secondary mineral deposits in mines, tunnels and on man-made structures. Hill and Forti more concisely defined "secondary minerals" which create speleothems in caves as;

A "secondary" mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus and/or deposited because of a unique set of conditions in a cave; i.e., the cave environment has influenced the mineral's deposition.

More than 250 cave mineral deposits exist. The vast majority of speleothems are calcareous, composed of calcium carbonate in the form of calcite or aragonite, or calcium sulfate in the form of gypsum. Calcareous speleothems form via carbonate dissolution reactions. Rainwater in the soil zone reacts with soil CO₂ to create weakly acidic water via the reaction:

As the lower pH water travels through the calcium carbonate bedrock from the surface to the cave ceiling, it dissolves the bedrock via the reaction:

When the solution reaches a cave, degassing due to lower cave pCO₂ drives precipitation of CaCO₃:

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