Speleothems: What are they made of & what make them colorful?

Speleothems, what we commonly call as cave formations, are secondary mineral deposits formed in the ceiling, floor, and walls of a cave through flowing, dripping and seeping of water.

The most commonly occurring minerals are calcite, aragonite, and gypsum although many other minerals have been found in speleothems (White, 2012). Further, the shapes and sizes of speleothems are dictated by how much minerals are carried by water flows, the details of water flow, and the unique deposition and crystal growth of the involved mineral.

Specifically, stalactites, stalagmites, flowstone, and other speleothems deposited from dripping for flowing water take shapes dictated by the details of the flow behavior (White, 2012). Interestingly, stalagmites are important climate archives and conserve climate information from the last 400,000 years. With this, stalagmites are generally selected for paleoclimatic analysis (Bradley, 2015).  On the other hand, White (2012) also cites that helictites, anthodites, and gypsum flowers are formed from seeping water and various pool deposits take shapes dictated by the habit of crystal growth.

Many factors impact the shape and color of speleothem formations including the rate and direction of water seepage, the amount of acid in the water, the temperature and humidity content of a cave, air currents, the above ground climate, the amount of annual rainfall and the density of the plant cover. Also, tan, orange, and brown colors common to calcite speleothems and also their luminescence under ultraviolet light is due to inclusion of humic and fulvic acid from overlying soils (White, 2012).

In conclusion, different caves offer different types of speleothems. So far, one of the must-see caves offering massive and plentiful speleothems is the Capisaan Cave in Kasibu, Nueva Vizcaya, Philippines.

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References

Bradley, R. S. (2015). Speleothems. In R. S. Bradley, Paleoclimatology: Reconstructing Climates of the Quaternary (3rd Ed.), (pp. 291-318). DOI: https://doi.org/10.1016/B978-0-12-386913-5.00008-9

White, W. (2012). Speleothems: General Overview. In W. White and D. Culver (Editors), Encyclopedia of Caves (2nd Ed.), (pp. 777). DOI: https://doi.org/10.1016/B978-0-12-383832-2.00113-4