A speleothem (; ) is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

made by

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

deposits A deposit account is a bank account maintained by a financial institution in which a customer can deposit and withdraw money. Deposit accounts can be savings accounts, current accounts or any of several other types of accounts explained below. ...

that accumulate over time in natural

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

s. Speleothems most commonly form in

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

caves due to carbonate dissolution reactions. They can take a variety of forms, depending on their depositional history and environment. Their chemical composition, gradual growth, and preservation in caves make them useful paleoclimatic proxies.

Chemical and physical characteristics

More than 300 variations of cave mineral deposits have been identified. The vast majority of speleothems are calcareous, composed of

calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

(CaCO₃) minerals (

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

aragonite Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (), the others being calcite and vaterite. It is formed by biological and physical processes, including precipitation fr ...

). Less commonly, speleothems are made of

calcium sulfate Calcium sulfate (or calcium sulphate) is an inorganic salt with the chemical formula . It occurs in several hydrated forms; the anhydrous state (known as anhydrite) is a white crystalline solid often found in evaporite deposits. Its dihydrate ...

(

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

mirabilite Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na2SO4·10H2O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is ...

) or

opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...

. Speleothems of pure calcium carbonate or calcium sulfate are translucent and colorless. The presence of

iron oxide An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust. Iron ...

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

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 Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

. 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

(CaCO₃) containing rocks such as

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

or dolomite, composed of

minerals. Carbonate minerals are more

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

in the presence of higher

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

(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: :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 In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

of CaCO₃ via the reaction: :Ca²⁺ + 2 HCO₃⁻ → CaCO₃ + H₂O + CO₂ Over time, the accumulation of these precipitates form dripstones (

stalagmite A stalagmite (, ; ; ) is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate, but may consist ...

stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...

s), and

flowstone Flowstones are sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are typically found in "solution caves", in limestone, where they are the most common speleothe ...

s, two of the major types of speleothems.

Climate proxies

Speleothem transects can provide paleoclimate records similar to those from ice cores or tree rings. Slow geometrical growth and incorporation of radioactive elements enables speleothems to be accurately and precisely dated over much of the late

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotop ...

and uranium-thorium dating, as long as the cave is a closed system and the speleothem has not undergone recrystallization. Oxygen ( δ¹⁸O) and carbon ( δ¹³C) stable isotopes are used to track variation in rainfall temperature, precipitation, and vegetation changes over the past ~500,000 years. The Mg/Ca proxy has likewise been used as a moisture indicator, although its reliability as a palaeohygrometer can be affected by cave ventilation during dry seasons. Variations in precipitation alter the width of speleothem rings: closed rings indicates little rainfall, wider spacing indicates heavier rainfall, and denser rings indicate higher moisture. Drip rate counting and trace element analysis of the water drops record short-term climate variations, such as

El Niño–Southern Oscillation El Niño–Southern Oscillation (ENSO) is a global climate phenomenon that emerges from variation in winds and sea surface temperatures over the tropical Pacific Ocean. Those variations have an irregular pattern but do have some semblance of cyc ...

(ENSO) climate events. Exceptionally, climate proxy data from the early

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

period have been retrieved from speleothems dated to 289 million years ago sourced from infilled caves exposed by quarrying at the Richards Spur locality in Oklahoma.

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:Hill, C A, and Forti, P, (1997). Cave Minerals of the World, (2nd edition). untsville, Alabama: National Speleological Society Inc.pp. 217, 225 * Dripstone is calcium carbonate in the form of stalactites or stalagmites **

Stalactite A stalactite (, ; , ) is a mineral formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble and that can be deposited as a colloid, or is in suspension (chemistry ...

s are pointed pendants hanging from the cave ceiling, from which they grow ***

Soda straw A soda straw (or simply straw) is a speleothem in the form of a hollow mineral cylinder (geometry), cylindrical tube. They are also known as tubular stalactites. Soda straws grow in places where water leaches slowly through cracks in rock, such ...

s are very thin but long stalactites with an elongated cylindrical shape rather than the usual more conical shape of stalactites ***

Helictite A helictite is a speleothem (cave-formed mineral) found in a Solution cave, limestone cave that changes its axis from the vertical at one or more stages during its growth. Helictites have a curving or angular form that looks as if they were gro ...

s 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 **

Stalagmite A stalagmite (, ; ; ) is a type of rock formation that rises from the floor of a cave due to the accumulation of material deposited on the floor from ceiling drippings. Stalagmites are typically composed of calcium carbonate, but may consist ...

s 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 ** Stalagnate results when stalactites and stalagmites meet or when stalactites reach the floor of the cave *

Flowstone Flowstones are sheetlike deposits of calcite or other carbonate minerals, formed where water flows down the walls or along the floors of a cave. They are typically found in "solution caves", in limestone, where they are the most common speleothe ...

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 * 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 In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

, rather than as secondary deposits. These include: ** Pillars ** Scallops ** Boneyard **

Boxwork In geology, boxwork is defined as a honeycomb-like structure that can form in some fractured or jointed sedimentary rocks. If the fractures in the host rock are mineralized, they can become more resistant to weathering than the surrounding rock, ...

* 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 ** Hells Bells, a particular speleothem found in the El Zapote

cenote A cenote ( or ; ) is a natural pit, or sinkhole, resulting when a collapse of limestone bedrock exposes groundwater. The term originated on the Yucatán Peninsula of Mexico, where the ancient Maya commonly used cenotes for water supplies, and ...

of Yucatan in the form of submerged, bell-like shapes ** Lava tubes contain speleothems composed of sulfates, mirabilite or opal. When the lava cools, precipitation occurs.

Calthemites

The usual definition of speleothem excludes secondary mineral deposits derived from

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

, lime, mortar, or other calcareous material (e.g. limestone and dolomite) outside the cave environment or in artificial caves (e.g. mines, tunnels), which can have similar shapes and forms as speleothems. Such secondary deposits in man-made structures are termed

calthemite Calthemite is a secondary deposit, derived from concrete, Lime (material), lime, Mortar (masonry), mortar or other calcareous material outside the cave environment.Smith, G.K. (2016). "Calcite straw stalactites growing from concrete structures" ...

s. Calthemites are often associated with concrete degradation, or due to leaching of lime, mortar, or other calcareous material.

Gallery

File:HallOfTheMountainKings.jpg, Various formations in the Hall of the Mountain Kings, Ogof Craig a Ffynnon,

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File:NaturalBridgeCaverns6.jpg, Stalactites and columns in Natural Bridge Caverns,

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

File:NaturalBridgeCaverns7.jpg, More formations in Natural Bridge Caverns,

File:Kl 0005356.jpg, Cave curtain formation in the Marble Arch Caves,

County Fermanagh County Fermanagh ( ; ) is one of the thirty-two counties of Ireland, one of the nine counties of Ulster and one of six counties of Northern Ireland. The county covers an area of and had a population of 63,585 as of 2021. Enniskillen is the ...

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File:CaliforniaCaveFormation.jpg, California Caverns, Calaveras County, California; one of many caverns located in the Sierra Foothills of California File:Dripstone column in Biserujka Cave, Dobrinj, Island of Krk.jpg, Stalagnates (columns) in the cave Biserujka, Dobrinj,

Island An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...

Krk,

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File:Druipsteen3.jpg, Various formations in the cave of Remouchamps, Aywaille,

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File:Zuil.jpg, Stalagnate (column) in the cave of Remouchamps, Aywaille,

File:Cave pearls.jpg, Image of Cave Pearl formation File:Flowstone in Mammoth Cave, KY.jpg, Image of flowstone in Mammoth Cave, KY

References

External links

The Virtual Cave: an online guide to speleothems

* ttps://web.archive.org/web/20130123003018/http://www.nature.nps.gov:80/geology/caves/photo_speleothems.htm Gallery of speleothemsfrom NPS Cave and Karst Program (archived on 23 January 2013) {{Caves Calcium minerals Dinaric Alps Dinaric karst formations Incremental dating Karst formations Karst Limestone Paleoclimatology Speleothems