Cave pearl

In this manner, concentric layers build up over time, in much the same way that a biological pearl forms within a mollusc.

[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.

The reason cave pearls tend to be round is not due to erosion by rotation, but rather that their growth is steady and uniform.

In addition to the typical spherical shape, cave pearls can be cylindrical, elliptical, cubical, hexagonal, discoid, or irregular.

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.

[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.