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Speleothem Article Draft
Speleothems,( /ˈspiːliːəθɛm/; Ancient Greek) are mineral deposits that accumulate over time within caves. The term speleothem, coined by Moore (1952), is derived from the Greek spēlaion "cave" + théma "deposit". Speleothems are most commonly composed of limestone, dolomite, and other calcium carbonate minerals. They can take a variety of forms, depending on their depositional history and environment. Due to their unique composition and gradual growth, they can be used as paleoclimate proxies.

Chemical composition
More than 250 variations of cave mineral deposits have been identified. The vast majority of speleothems are calcareous, composed of calcium carbonate (CaCO3) in the form of calcite or aragonite. Less commonly, speleothems are composed of gypsum, mirabilite, or opal.

The coloring of speleothems depends on their composition. Speleothems of pure calcium carbonate and 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.

Formation
Carbonate speleothems form via dissolution of limestone or dolomite during reactions with acidic groundwater, and reprecipitation of calcium carbonate minerals in cave formations. Rainwater reacts with carbon dioxide in soil to create slightly acidic water:


 * H2O + CO2 → H2CO3

As the low pH water travels down through calcium carbonate bedrock, it dissolves the carbonate bedrock via the reaction:


 * CaCO3 + H2CO3 → Ca2+ + 2 HCO3−

When the solution reaches the cave ceiling, the lower pCO2 in the cave drives precipitation of calcium carbonate minerals due to CO2 degassing:


 * Ca2+ + 2 HCO3− → CaCO3 + H2O + CO2

Many factors impact the formation of speleothems, 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.

Over time, the accumulation of these mineral precipitates form stalagmites, stalactites, and flowstones, which compose the major categories of speleothems.

Types and categories
[[File:Tropfsteine.svg|thumb|• A Stalactite

• B Soda straws

• C Stalagmites

• D Coned stalagmite

• E Stalagnate or column

• F Drapery

• G Drapery

• H Helictites

• I Moonmilk

• J Sinter pool, rimstone

• K Calcite crystals

• L Sinter terrace

• M Karst

• N Body of water

• O Shield

• P Cave clouds

• Q Cave pearls

• R Tower cones

• S Shelfstones

• T Baldacchino canopy

• U Bottlebrush stalactite

• V Conulite

• W Flowstone

• X Trays

• Y Calcite rafts

• Z Cave popcorn or coralloids

• AA Frostworks

• AB Flowstone

• AC Splattermite

• AD Speleoseismites

• AE Boxworks

• AF Oriented stalactite

• AG collapsed rubble]] 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:


 * 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
 * Columns result when stalactites and stalagmites meet or when stalactites reach the floor of the cave
 * Flowstone_in_Mammoth_Cave,_KY.jpgFlowstone 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
 * 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, and are formed by segregation of solutes during the 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
 * Hells Bells, a particular speleothem found in the El Zapote cenote 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.

As climate proxies
Speleothems are studied as climate proxies because their location within cave environments and patterns of growth allow them to be used as archives for several climate variables. By sampling along a dated transect of a speleothem, speleothems chemical composition and growth rates provide paleoclimate records similar to those from ice cores. Variations in precipitation alter the width of new ring formation, where closed ring formation shows little rainfall, and wider spacing shows heavier rainfall. Denser speleothems indicates higher moisture availability.

The principal proxies that are recorded in speleothems include stable isotopes of oxygen (δ18O) and carbon (δ13C), giving high-resolution data that can show annual variation in rainfall temperature and precipitation. These indicators, alone and in conjunction with other climate proxy records, can provide clues to past precipitation, temperature, and vegetation changes over the last ~500,000 years.

The geometrical way in which stalagmites grow, which varies based on the height the water is falling from and the rate of flow, is also used in paleoclimate applications. Weaker flows and short travel distances form narrower stalagmites, while heavier flow and a greater fall distance tend to form broader ones. Additionally, drip rate counting and trace element analysis of the water drops themselves have been shown to record shorter-term variations in the climate at high resolution, such as drought conditions attributed to the El Niño–Southern Oscillation (ENSO) climate events.

A particular strength of speleothems for paleoclimate proxies is their unique ability to be accurately and precisely dates over much of the late Quaternary by radiocarbon dating and uranium-thorium dating. For accurate dating, the speleothem must have been in a closed system without recrystallization.

Calthemites: secondary deposits not formed in caves
Secondary deposits derived from concrete, lime, mortar, or calcareous material as found on man-made structures outside the cave environment or in artificial caves (e.g. mines and tunnels), can mimic the shapes and forms of speleothems, but are classed as calthemites. The occurrence of calthemites is often associated with concrete degradation, but could also be linked to leaching of lime, mortar or other calcareous material (e.g. limestone and dolomite). Despite similar appearances, "calthemites" (created outside the cave environment) are not considered to be "speleothems" (created inside the cave environment), and vice versa, as per their definitions.