Speleothems

Speleothems are mineral deposits that form in caves as groundwater loses carbon dioxide and precipitates minerals. They develop mainly in carbonate rocks such as limestone or dolomite. The dominant mineral is calcite (calcium carbonate), though aragonite occurs in some deposits. As water enters a cave, CO2 escapes, reducing solubility and causing calcite to crystallize on surfaces such as ceilings, floors, and walls over long times.

Common forms include stalactites (hanging from ceilings), stalagmites (rising from floors), and columns where a stalactite and stalagmite join. Flowstones create sheet-like blankets on walls or floors; curtains and draperies trail along fissures. Other types include helictites, which grow in irregular directions; soda straws, slender hollow tubes; cave popcorn; and cave pearls formed in pools. Gypsum caves host gypsum speleothems as well.

Growth rates are slow, often millimeters per year or less, recording long histories. Speleothems are valuable archives for paleoclimate studies and can be dated by radiometric methods and analyzed for isotopic composition and trace elements. They also reflect modern cave conditions and can respond to climate, air exchanges, and human disturbance.

Because speleothems are fragile, they are protected in most caves. Touching formations, vibrations, and changes in cave ventilation can halt growth or dissolve features. Responsible access, monitoring, and education help preserve these natural records while enabling scientific and educational use.