Helictites (Buchanan 2025)

Helictites are a type of solidified speleothem, usually tortuous formations that occur in some caves. Typically composed of dimorphic calcium carbonate (CaCO3). On occasion aragonite can precipitate in low energy systems. They are characterised by their twisted, curved, or helical shape, often appearing as if they have grown in defiance of gravity.

The formation of helictites is not fully understood, but it is believed to involve a combination of factors, including:

  • The slow dripping of mineral-rich water, which deposits CaCO3 as it evaporates or comes into contact with the cave air.
  • The presence of microorganisms, such as bacteria, which may play a role in the precipitation of CaCO3, chemotaxis can influence the trajectory of growth. 
  • The unique chemistry, climate and physics of the cave environment, including factors such as temperature, humidity, and air currents.

Helictites can form through a variety of mechanisms, including:

  • Dripstone formation, where mineral-rich water drips from the ceiling of the cave, depositing CaCO3 as it falls.
  • Flowstone formation, where mineral-rich water flows over the surface of the cave speleothem, depositing CaCO3 as water moves cyclically.
  • Pool fingers, where mineral-rich water accumulates in pools on the cave floor, depositing CaCO3 as it evaporates cyclically.

The CaCO3 that makes up helictites is typically deposited in the form of calcite, which is a mineral composed of calcium, carbon, and oxygen atoms. The chemical formula for calcite being CaCO3, it is one of the most common minerals found in carbonate caves and other karst environments.

Photographs by Buchanan – Apologies, the exposure levels are erratic in some of these examples. In some cases, they are taken on the fly when your balance is precarious…

References

  • Hill, C. A., & Forti, P. (1997). Cave minerals of the world. National Speleological Society.
  • Kendall, A. C. (1985). Radiaxial fibrous calcite: a re-examination. Journal of Sedimentary Petrology, 55(4), 519-528.
  • Folk, R. L. (1993). SEM imaging of bacteria and nanobacteria in carbonate sediments and rocks. Journal of Sedimentary Petrology, 63(3), 990-999.
  • Davis, D. G. (1980). Cave geology. National Speleological Society.
  • White, W. B. (2007). Cave sediments and speleothems. In Encyclopedia of Caves (pp. 143-151). Academic Press.
  • Tisato, N. et al. (2015) Microbial mediation of complex subterranean mineral structures. Sci. Rep. 5, 15525; doi: 10.1038/srep15525

 

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