speleothem

A speleothem is a secondary mineral deposit formed in caves by the precipitation of minerals from groundwater. The term derives from Greek spele (cave) and thesma or thema (deposit). Most speleothems consist of calcium carbonate minerals, primarily calcite, but some gypsum caves form gypsum deposits as well. They arise when mineral-rich water moves through the rock, degasses carbon dioxide, and becomes supersaturated with calcium carbonate, causing calcite to precipitate in solid form.

Common forms include stalactites, which hang from the ceiling; stalagmites, which rise from the floor; and columns or pillars when a stalactite and stalagmite meet. Other well-known forms are flowstones, which create sheet-like formations on walls or floors; draperies and curtains that hang along spaces; cave popcorn or coralloids; soda straws, thin hollow tubes; and helictites, which grow in irregular, twisting shapes. While calcite is most prevalent, other minerals such as aragonite or gypsum can form speleothems under appropriate conditions.

Formation occurs over long timescales as water percolates through rock, precipitating minerals in place. Growth rates are typically slow, ranging from fractions of a millimeter to a few millimeters per year, depending on humidity, temperature, airflow, and mineral saturation. Speleothems are valuable archives of past environmental and climatic conditions, allowing isotopic and radiometric dating to reconstruct paleoclimate records. They are also sensitive to disturbance; handling or vandalism can halt growth and permanently damage the deposits.