speleothemen

Speleothemen (German plural for speleothem) are secondary mineral deposits formed in caves by the precipitation of minerals from groundwater. The most common material is calcium carbonate, deposited as calcite, but some speleothemen are gypsum or aragonite. They form when water dripping or flowing in a cave loses carbon dioxide and becomes supersaturated with respect to the mineral, causing crystals to precipitate. Growth occurs slowly, typically millimetres per century, varying with temperature, humidity, water supply, and gas content.

Common forms include stalactites (icicle-shaped features hanging from ceilings), stalagmites (rising from floors), and columns when the two meet. Flowstones cover floors or walls with smooth sheets; helictites grow in twisting directions; soda straws are slender, hollow stalactites. Other features include curtains, cave pearls, and boxwork. In gypsum caves, gypsum speleothems (gypsum crystals, crystal rosettes) occur.

Speleothemen provide records of past climates through isotopic composition of the calcite and can be dated using methods such as uranium–lead or uranium–thorium dating, among others. They form in stable microclimates and are sensitive to disturbance. They are found in many karst regions worldwide, with notable examples where carbonate rocks are abundant.

Conservation and study: they are fragile and can be damaged by touch, changes in humidity, or vibrations from visitors; preservation guidelines emphasize not touching and limiting lighting and CO2 input. They are of interest to scientists for paleoclimate reconstruction and to visitors for natural beauty. Preservation depends on maintaining cave microclimates and minimizing external disturbances.