Speleothem
A speleothem (
Chemical and physical characteristics
More than 300 variations of cave mineral deposits have been identified.[2] The vast majority of speleothems are calcareous, composed of calcium carbonate (CaCO3) minerals (calcite or aragonite). Less commonly, speleothems are made of calcium sulfate (gypsum or mirabilite) or opal.[2] Speleothems of pure calcium carbonate or calcium sulfate are translucent and colorless. The presence of iron oxide or copper provides a reddish brown color. The presence of manganese oxide can create darker colors such as black or dark brown. Speleothems can also be brown due to the presence of mud and silt.[2]
Many factors impact the shape and color of speleothems, including the chemical composition of the rock and water, water seepage rate, water flow direction, cave temperature, cave humidity, air currents, aboveground climate, and aboveground plant cover. Weaker flows and short travel distances form narrower stalagmites, while heavier flow and a greater fall distance tend to form broader ones.
Formation processes
Most cave chemistry involves calcium carbonate (CaCO3) containing rocks such as limestone or dolomite, composed of calcite or aragonite minerals. Carbonate minerals are more soluble in the presence of higher carbon dioxide (CO2) and lower temperatures. Calcareous speleothems form via carbonate dissolution reactions whereby rainwater reacts with soil CO2 to create weakly acidic water via the reaction:[3]
- H2O + CO2 → H2CO3
As the acidic water travels through the calcium carbonate bedrock from the surface to the cave ceiling, it dissolves the bedrock via the reaction:
- CaCO3 + H2CO3 → Ca2+ + 2 HCO3−
When the solution reaches a cave, the lower pCO2 in the cave drives the precipitation of CaCO3 via the reaction:
- Ca2+ + 2 HCO3− → CaCO3 + H2O + CO2
Over time, the accumulation of these precipitates form dripstones (stalagmites, stalactites), and flowstones, two of the major types of speleothems.
Climate proxies
Speleothem transects can provide paleoclimate records similar to those from
Types and categories
Speleothems take various forms, depending on whether the water drips, seeps, condenses, flows, or ponds. Many speleothems are named for their resemblance to man-made or natural objects. Types of speleothems include:[11]
- Dripstone is calcium carbonate in the form of stalactites or stalagmites
- Stalactites are pointed pendants hanging from the cave ceiling, from which they grow
- Soda straws are very thin but long stalactites with an elongated cylindrical shape rather than the usual more conical shape of stalactites
- Helictites are stalactites that have a central canal with twig-like or spiral projections that appear to defy gravity
- Include forms known as ribbon helictites, saws, rods, butterflies, hands, curly-fries, and "clumps of worms"
- Chandeliers are complex clusters of ceiling decorations
- Ribbon stalactites, or simply "ribbons", are shaped accordingly
- Stalagmites are the "ground-up" counterparts of stalactites, often blunt mounds
- Broomstick stalagmites are very tall and spindly
- Totem pole stalagmites are also tall and shaped like their namesakes
- Fried egg stalagmites are small, typically wider than they are tall
- Stalagnateresults when stalactites and stalagmites meet or when stalactites reach the floor of the cave
- Stalactites are pointed pendants hanging from the cave ceiling, from which they grow
- Flowstone is sheet like and found on cave floors and walls
- Draperies or curtains are thin, wavy sheets of calcite hanging downward
- Bacon is a drapery with variously colored bands within the sheet
- Rimstone dams, or gours, occur at stream ripples and form barriers that may contain water
- Stone waterfall formations simulate frozen cascades
- Draperies or curtains are thin, wavy sheets of calcite hanging downward
- Cave crystals
- Dogtooth spar are large calcite crystals often found near seasonal pools
- Frostwork is needle-like growths of calcite or aragonite
- Moonmilk is white and cheese-like
- Anthodites are flower-like clusters of aragonite crystals
- Cryogenic calcite crystals are loose grains of calcite found on the floors of caves formed by segregation of solutes during freezing of water.
- Speleogens (technically distinct from speleothems) are formations within caves that are created by the removal of bedrock, rather than as secondary deposits. These include:
- Pillars
- Scallops
- Boneyard
- Boxwork
- Others
- Cave popcorn, also known as "coralloids" or "cave coral", are small, knobby clusters of calcite
- Cave pearls are the result of water dripping from high above, causing small "seed" crystals to turn over so often that they form into near-perfect spheres of calcium carbonate
- Snottites are colonies of predominantly sulfur oxidizing bacteria and have the consistency of "snot", or mucus
- Calcite rafts are thin accumulations of calcite that appear on the surface of cave pools
- Yucatanin the form of submerged, bell-like shapes
- Lava tubescontain speleothems composed of sulfates, mirabilite or opal. When the lava cools, precipitation occurs.
Calthemites
The usual definition of speleothem excludes
Gallery
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Various formations in the Hall of the Mountain Kings, Ogof Craig a Ffynnon, South Wales, Great Britain
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Stalactites and columns in Natural Bridge Caverns, Texas
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More formations in Natural Bridge Caverns, Texas
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Sierra Foothillsof California
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Image of Cave Pearl formation
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Image of flowstone in Mammoth Cave, KY
See also
References
- ISBN 9780128141243.
- ^ ISSN 0583-6050.
- )
- ISBN 978-0-12-386913-5.
- ISSN 1529-6466.
- .
- .
- PMC 6434041. Retrieved 30 September 2023.
- ISSN 1944-8007.
- ISSN 0091-7613.
- ^ Hill, C A, and Forti, P, (1997). Cave Minerals of the World, (2nd edition). [Huntsville, Alabama: National Speleological Society Inc.] pp. 217, 225
External links
- The Virtual Cave: an online guide to speleothems
- Mineral aggregates from carst caves, formed in capillary film solutions
- Gallery of speleothems from NPS Cave and Karst Program (archived on 23 January 2013)