Cave pearls are small, spherical calcite formations the size of marbles that are formed by the concentric deposition of calcium salts around a nucleus such as a grain of sand. As its name suggests, cave pearls occur only in caves - limestone caves, to be specific. Exposure to moving water polishes the surface of cave pearls, making them glossy, just like real pearls. While cave pearls are relatively common in caves, they are typically present in very low numbers. Gruta de las Canicas - a system of caves in Tabasco, Mexico, is highly unusual in this regard for it contains a tremendous quantity of pearls. It is estimated that the cave contains some 200 million pearls that cover the cave floor to a depth of more than a meter.

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