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Cave pearl
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.
== Composition ==
A cave pearl is composed primarily of calcite. Cave pearls are generally not considered to be a type of oolite. Other minerals found in small quantities in cave pearls include quartz, apatite, iron, aluminum, and magnesium.〔http://www.karstportal.org/FileStorage/NSS_news/1956-v014-008.pdf〕〔https://gsa.confex.com/gsa/2008AM/finalprogram/abstract_150967.htm〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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