Cave pearl

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Carlsbad Caverns, New Mexico

A cave pearl is a small, usually spherical,

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.

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, aluminium, and magnesium.[1][2]

Formation

Diagram of dripstone cave structures (cave pearls labeled Q)

Cave pearls form when water dripping into a cave loses

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

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]

References

  1. ^ a b NSS News. 14 (8). National Speleological Society. 1956 http://www.karstportal.org/FileStorage/NSS_news/1956-v014-008.pdf. {{cite journal}}: Missing or empty |title= (help) [dead link]
  2. ^ a b 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. 40 (6). Geological Society of America: 479.
  3. doi:10.5038/1827-806X.40.2.1
    .
  4. ^ NSS News. 16 (10). National Speleological Society. 1958 http://www.karstportal.org/FileStorage/NSS_news/1958-v016-010.pdf. {{cite journal}}: Missing or empty |title= (help) [dead link]
  5. ^ NSS News. 13 (10). National Speleological Society. 1955 http://www.karstportal.org/FileStorage/NSS_news/1955-v013-010.pdf. {{cite journal}}: Missing or empty |title= (help) [dead link]
  6. ^ a b "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.

External links

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