What are cave pearls?
A cave pearl is a small, usually spherical, (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.
Cave pearls form when water dripping into a cave loses carbon dioxide and precipitates calcite. 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.
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. 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".
A cave pearl is composed primarily of calcite (calcium carbonate). 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), apatite (a group of phosphate minerals), iron, aluminum, and magnesium.
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