Cave popcorn

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Cave popcorn with frostwork Popcorn-with-Frostwork.jpg
Cave popcorn with frostwork

Cave popcorn, or coralloids, are small nodes of calcite, aragonite or gypsum that form on surfaces in caves, especially limestone caves. [1] [2] They are a common type of speleothem. [1] [2]



Cave popcorn trays Cave popcorn trays.jpg
Cave popcorn trays

The individual nodules of cave popcorn range in size from 5 to 20 mm and may be decorated by other speleothems, especially aragonite needles or frostwork. [1] [2] The nodules tend to grow in clusters on bedrock or the sides of other speleothems. [1] These clusters may terminate suddenly in either an upward or downward direction, forming a stratographic layer. [1] When they terminate in a downward direction, they may appear as flat bottomed formations known as trays. [1]

Individual nodes of popcorn can assume a variety of shapes from round to flattened ear or button like shapes. [2]

The color of cave popcorn is usually white, but various other colors are possible depending on the composition. [2]


Button cave popcorn Button cave popcorn.jpg
Button cave popcorn

Cave popcorn can form by precipitation. [1] Water seeping through limestone walls or splashing onto them leaves deposits when CO2 loss causes its minerals to precipitate. [2] When formed in this way, the resultant nodules have the characteristics of small balls of flowstone. [1]

Cave popcorn can also form by evaporation in which case it is chalky and white like edible popcorn. [1] In the right conditions, evaporative cave popcorn may grow on the windward side of the surface to which it is attached or appear on the edges of projecting surfaces. [1]

Alisadr Cave, Hamedan, Iran Alisadr Cave, Hamedan, Iran.JPG
Alisadr Cave, Hamedan, Iran

On manmade structures (outside the cave environment)

Popcorn can also occur on concrete structures outside the cave environment; these are classified as calthemite coralloids. Calthemite coralloids also occur in "artificial caves" such as mines or railway or vehicle tunnels were there is a source of lime, mortar or cement from which the calcium ions can be leached.

Coralloids can form by a number of different methods in caves; however, the most common form on concrete is created when a hyperalkaline solution seeps from fine cracks. Due to solution evaporation, deposition of calcium carbonate occurs before any drop can form. The resulting coralloids are small and chalky with a cauliflower appearance.[ citation needed ]

Calthemite coralloids growing on underside of concrete structure and straw stalactite Calthemite coralloids.jpg
Calthemite coralloids growing on underside of concrete structure and straw stalactite

Related Research Articles

Limestone Sedimentary rocks made of calcium carbonate

Limestone is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3). A closely related rock is dolomite, which contains a high percentage of the mineral dolomite, CaMg(CO3)2. In old USGS publications, dolomite was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolomites or magnesium-rich limestones.

Stalactite elongated mineral formation which hangs down from a cave ceiling

A stalactite is a type of formation that hangs from the ceiling of caves, hot springs, or manmade structures such as bridges and mines. Any material that is soluble, can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of lava, minerals, mud, peat, pitch, sand, sinter, and amberat. A stalactite is not necessarily a speleothem, though speleothems are the most common form of stalactite because of the abundance of limestone caves.

Aragonite carbonate mineral

Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, CaCO3 (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including precipitation from marine and freshwater environments.

Stalagmite elongated mineral formation which forms on a cave floor

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 may be composed of lava, minerals, mud, peat, pitch, sand, sinter and amberat.

Travertine A form of limestone deposited by mineral springs

Travertine is a form of limestone deposited by mineral springs, especially hot springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a process of rapid precipitation of calcium carbonate, often at the mouth of a hot spring or in a limestone cave. In the latter, it can form stalactites, stalagmites, and other speleothems. It is frequently used in Italy and elsewhere as a building material.

Speleothem A structure formed in a cave by the deposition of minerals from water

Speleothems, commonly known as cave formations, are secondary mineral deposits formed in a cave. Speleothems typically form in limestone or dolomite solutional caves. The term "speleothem," as first introduced by Moore (1952), is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem," in most publications, specifically excludes secondary mineral deposits in mines, tunnels, and other man-made structures. Hill and Forti more concisely defined "secondary minerals" which create speleothems in caves:

A "secondary" mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus, and/or deposited because of a unique set of conditions in a cave; i.e., the cave environment has influenced the mineral's deposition.

Soda straw

A soda straw is a speleothem in the form of a hollow mineral cylindrical tube. They are also known as tubular stalactites. Soda straws grow in places where water leaches slowly through cracks in rock, such as on the roofs of caves. Soda straws in caves rarely grow more than a few millimetres per year and may average one tenth of a millimetre per year. A soda straw can turn into a stalactite if the hole at the bottom is blocked, or if the water begins flowing on the outside surface of the hollow tube.

Dolomite (rock) Sedimentary carbonate rock that contains a high percentage of the mineral dolomite

Dolomite (also known as dolostone, dolomite rock or dolomitic rock) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. In old USGS publications, it was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolomites or magnesium-rich limestones. Dolomite has a stoichiometric ratio of nearly equal amounts of magnesium and calcium. Most dolomites formed as a magnesium replacement of limestone or lime mud before lithification. Dolomite is resistant to erosion and can either contain bedded layers or be unbedded. It is less soluble than limestone in weakly acidic groundwater, but it can still develop solution features (karst) over time. Dolomite can act as an oil and natural gas reservoir.


Flowstones are composed of 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 speleothem. However, they may form in any type of cave where water enters that has picked up dissolved minerals. Flowstones are formed via the degassing of vadose percolation waters.

Efflorescence migration of a salt to the surface of a porous material

In chemistry, efflorescence is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an internally held salt in water, or occasionally in another solvent. The water, with the salt now held in solution, migrates to the surface, then evaporates, leaving a coating of the salt.

Calcium bicarbonate, also called calcium hydrogen carbonate, has a chemical formula Ca(HCO3)2. The term does not refer to a known solid compound; it exists only in aqueous solution containing the calcium (Ca2+), bicarbonate (HCO
), and carbonate (CO2−
) ions, together with dissolved carbon dioxide (CO2). The relative concentrations of these carbon-containing species depend on the pH; bicarbonate predominates within the range 6.36–10.25 in fresh water.

Cave of the Mounds cave in United States of America

Cave of the Mounds, a natural limestone cave located near Blue Mounds, Wisconsin, United States, is named for two nearby hills called the Blue Mounds. It is located in the southern slope of the east hill. The cave's beauty comes from its many varieties of mineral formations called speleothems. The Chicago Academy of Sciences considers the Cave of the Mounds to be "the significant cave of the upper Midwest" because of its beauty, and it is promoted as the "jewel box" of major American caves. In 1987, the United States Department of the Interior and the National Park Service designated the cave as a National Natural Landmark.


Anthodites (Greek ἄνθος ánthos, "flower", -ode, adjectival combining form, -ite adjectival suffix) are speleothems (cave formations) composed of long needle-like crystals situated in clusters which radiate outward from a common base. The "needles" may be quill-like or feathery. Most anthodites are made of the mineral aragonite (a variety of calcium carbonate, CaCO3), although some are composed of gypsum (CaSO4·2H2O).


In geology, frostwork is a type of speleothem with acicular ("needle-like") growths almost always composed of aragonite or calcite replaced aragonite. It is a variety of anthodite. In some caves frostwork may grow on top of cave popcorn or boxwork.


Rimstone, also called gours, is a type of speleothem in the form of a stone dam. Rimstone is made up of calcite and other minerals that build up in cave pools. The formation created, which looks like stairs, often extends into flowstone above or below the original rimstone. Often, rimstone is covered with small, micro-gours on horizontal surfaces. Rimstone basins may form terraces that extend over hundreds of feet, with single basins known up to 200 feet long from Tham Xe Biang Fai in Laos

Solutional cave cave formed in soluble rock such as limestone, chalk, dolomite, marble, salt beds or gypsum

A solutional cave or karst cave is a cave usually formed in the soluble rock limestone. It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.

Concrete degradation Concrete technology

Concrete degradation may have various causes. Concrete can be damaged by fire, aggregate expansion, sea water effects, bacterial corrosion, calcium leaching, physical damage and chemical damage. This process adversely affects concrete exposed to these damaging stimuli.

Calcite rafts

Calcite crystals form on the surface of quiescent bodies of water, even when the bulk water is not supersaturated with respect to calcium carbonate. The crystals grow, attach to one other and appear to be floating rafts of a white, opaque material. The floating materials have been referred to as calcite rafts or "leopard spots".

Coralloid (coral-shaped) may refer to:

Calthemite Secondary calcium carbonate deposit growing under man-made structures

Calthemite is a secondary deposit, derived from concrete, lime, mortar or other calcareous material outside the cave environment. Calthemites grow on or under, man-made structures and mimic the shapes and forms of cave speleothems, such as stalactites, stalagmites, flowstone etc. Calthemite is derived from the Latin calx "lime" + Latin < Greek théma, "deposit" meaning ‘something laid down’, and the Latin –ita < Greek -itēs – used as a suffix indicating a mineral or rock. The term "speleothem", due to its definition can only be used to describe secondary deposits in caves and does not include secondary deposits outside the cave environment.


  1. 1 2 3 4 5 6 7 8 9 10 Palmer, Arthur N. (2007). Cave Geology. Dayton, OH: CAVE BOOKS. p. 288. ISBN   978-0-939748-66-2.
  2. 1 2 3 4 5 6 Hill, Carol; Forti, Paolo (1997). Cave Minerals of the World (Second Edition ed.). Huntsville, AL: National Speleological Society. pp. 59–61. ISBN   1-879961-07-5.