Cave pearl

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A nest of cave pearls in Carlsbad Caverns, New Mexico Cave Pearls.JPG
A nest of cave pearls in Carlsbad Caverns, New Mexico

A cave pearl is a small, usually spherical, speleothem (cave formation) found in limestone caves. Cave pearls are formed by a concretion of calcium salts that form concentric layers around a nucleus. Exposure to moving water polishes the surface of cave pearls, making them glossy; if exposed to the air, cave pearls can degrade and appear rough.

Contents

Composition

A cave pearl is composed primarily of calcite (calcium carbonate [CaCO3]). Cave pearls are generally not considered to be a type of oolite. Other minerals found in small quantities in cave pearls include quartz (silicon dioxide [SiO2]), apatite (a group of phosphate minerals), iron, aluminum, and magnesium. [1] [2]

Formation

Diagram of dripstone cave structures (cave pearls labeled Q) Tropfsteine.svg
Diagram of dripstone cave structures (cave pearls labeled Q)

Cave pearls form when water dripping into a cave loses carbon dioxide and precipitates calcite. A cave pearl forms when the water is moving too vigorously to form a stalagmite. A nucleus of matter (such as a grain of sand) becomes coated with calcite, and the current then provides a rotation to the nucleus in such a way that it is coated evenly. In this manner, concentric layers build up over time, in much the same way that a biological pearl forms within a mollusc. There may be microbial action involved in the formation of cave pearls. [3]

The existence of an actual pool may not be necessary for cave pearls to form, as long as the deposit is kept wet and agitated by water dripping or trickling through. [4] If the cave pearl sinks to the bottom of a pool or is otherwise in direct contact with moving water, the motion of the water buffs it to a high gloss. Although the motion of the water often keeps cave pearls from adhering, sometimes cave pearls will stick to one another or to the bottom of a pool.

Nucleus

A cave pearl forms around a nucleus of matter. The nucleus of a cave pearl is typically very small, such as a grain of sand, but can be larger. [5] Some nuclei are made of foreign matter (such as quartz sand, wood, bone, or even plastic), whereas others are made of calcified clay or limestone. [1]

Shape

Cave pearls are usually spherical but can also have other shapes. The reason cave pearls tend to be round is not due to erosion by rotation, but rather that their growth is steady and uniform. Because a spherical shape allows the greatest amount of deposition for the smallest surface area, a cave pearl tends to end up spherical even if its nucleus is highly irregular. Sometimes several cave pearls stick together to form a shape that resembles a bunch of grapes. In addition to the typical spherical shape, cave pearls can be cylindrical, elliptical, cubical, hexagonal, discoid, or irregular. [6]

Size

Most cave pearls are smaller than 1 cm (0.39 in) wide. Large cave pearls grow as big as 20 cm (7.9 in) in diameter. The world's largest cave, Son Doong Cave in Vietnam, has cave pearls "the size of baseballs". [7]

Frequency

Cave pearls are relatively common in caves but are typically present in low abundance.

In Tabasco, Mexico, the Gruta de las Canicas (Cave of the Marbles) is highly unusual in that it contains a tremendous quantity of pearls: an estimated 200 million pearls were discovered on the cave floor, in some areas to a depth of a meter or more. The mechanism for the formation of this vast quantity of pearls has not been determined. [2]

The Rookery, in Carlsbad Caverns, New Mexico, has so many cave pearls that they were at one time handed out to visitors as souvenirs. [6]

Related Research Articles

Stalactite Elongated mineral formation hanging down from a cave ceiling

A stalactite (, ; from the Greek 'stalaktos' via stalassein, 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, 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.

Stalagmite Elongate mineral formation found 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 are typically composed of calcium carbonate, but may consist of lava, mud, peat, pitch, sand, sinter and amberat.

National Speleological Society Organization for exploration, conservation, and study of caves in the United States

The National Speleological Society (NSS) is an organization formed in 1941 to advance the exploration, conservation, study, and understanding of caves in the United States. Originally headquartered in Washington D.C., its current offices are in Huntsville, Alabama. The organization engages in the research and scientific study, restoration, exploration, and protection of caves. It has more than 10,000 members in more than 250 grottos.

Concretion Compact mass formed by precipitation of mineral cement between particles

A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin concretio "(act of) compacting, condensing, congealing, uniting", itself from con meaning 'together' and crescere meaning "to grow". Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum.

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

A speleothem is a geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous 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.

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. Soda straws can also form outside the cave environment on exposed concrete surfaces as a type of calthemite, growing significantly faster than those formed on rock.

Lava tube Natural conduit through which lava flows beneath the solid surface

A lava tube, or pyroduct, is a natural conduit formed by flowing lava from a volcanic vent that moves beneath the hardened surface of a lava flow. If lava in the tube empties, it will leave a cave.

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

Dolomite (also known as dolomite rock, dolostone or dolomitic rock) is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite, CaMg(CO3)2. It occurs widely, often in association with limestone and evaporites, though it is less abundant than limestone and rare in Cenozoic rock beds (beds less than about 65 million years in age). The first geologist to distinguish dolomite rock from limestone was Belsazar Hacquet in 1778.

Flowstone

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.

Cave popcorn Small nodes of calcite, aragonite or gypsum that form on surfaces in caves

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

Cave of the Mounds

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.

Borra Caves Place in Andhra Pradesh, India

The Borra Caves, also called Borra Guhalu, are located on the East Coast of India, in the Ananthagiri hills of the Araku Valley of the Visakhapatnam district in Andhra Pradesh. The caves, one of the largest in the country, at an elevation of about 705 m (2,313 ft), distinctly exhibit a variety of speleothems ranging in size and irregularly shaped stalactites and stalagmites. The caves are basically karstic limestone structures extending to a depth of 80 m (260 ft), and are considered the deepest caves in India.

Shelfstone Shelf-like speleothem set upon sessile streams

Shelfstone is a type of speleothem that grows inwards from the edge of a cave pool. It takes the form of ledges that tend to be flat on top and sloping underneath. They are almost always formed from calcite, when materials precipitated from dripping water onto a cave pool attach to the side. The deposition continues to grow laterally, underneath. The shelfstone above the current water level in a pool is an indicator of past levels of the pool. Shelfstone can be very thick when the water level has stayed constant over a long period of time. If the water level is constantly changing, the shelfstone will be thin and delicate.

Rimstone

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.

Castellana Caves

The Castellana Caves are a karst cave system located in the municipality of Castellana Grotte, in the Metropolitan City of Bari, Apulia, southern Italy.

Cave of El Soplao

El Soplao is a cave located in the municipalities of Rionansa, Valdáliga and Herrerías in Cantabria, Spain. It is considered unique for the quality and quantity of geological formations (speleothems) in its 17 miles length, 6 of which are open to the public. In it are formations such as helíctites and curtains. Its formation dates back to the Mesozoic, in particular the Cretaceous period 240 million years ago. The entrance is at 540 metres in the Sierra Soplao Arnero.

Calcite rafts Cave-crystallized calcite crusts

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".

Gruta da Lagoa Azul State Park

The Gruta da Lagoa Azul State Park is a state park in the state of Mato Grosso, Brazil. Its primary attraction is a limestone cave with a pool of blue water and unusual cave formations. These have suffered from vandalism, causing the cave to be closed until measures to protect it could be implemented.

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.

Diamond Caverns in Park City, Kentucky was discovered on July 14, 1859. Tours are available year around; closed Thanksgiving, Christmas Eve, and Christmas. Tours last one hour and is a half mile round trip.

References

  1. 1 2 NSS News(PDF). National Speleological Society. 14 (8). 1956 http://www.karstportal.org/FileStorage/NSS_news/1956-v014-008.pdf.Missing or empty |title= (help)[ dead link ]
  2. 1 2 Houston, Shari; Mozley, Peter S.; Campbell, Andrew R.; Boston, Penny. "Petrology and Chemistry of Cave Pearls from Gruta De Las Canicas (Cave of the Marbles), Tabasco, Mexico". Abstracts with Programs. Geological Society of America. 40 (6): 479.
  3. Onac, Bogdan P.; Forti, Paolo (July 2011). "Minerogenetic mechanisms occurring in the cave environment: an overview". International Journal of Speleology . 40 (2): 79–98. doi: 10.5038/1827-806X.40.2.1 .
  4. NSS News(PDF). National Speleological Society. 16 (10). 1958 http://www.karstportal.org/FileStorage/NSS_news/1958-v016-010.pdf.Missing or empty |title= (help)[ dead link ]
  5. NSS News(PDF). National Speleological Society. 13 (10). 1955 http://www.karstportal.org/FileStorage/NSS_news/1955-v013-010.pdf.Missing or empty |title= (help)[ dead link ]
  6. 1 2 "Underground: What and Who are in Caves?". National Park Service. Archived from the original on February 25, 2013. Retrieved September 9, 2013.
  7. Jenkins, Mark (January 2011). "Vietnam Cave". National Geographic . p. 7. Archived from the original on December 20, 2010.