1. Carbonate concretion, usually of calcite, that is spherical or irregular in shape, with an internal structure of concentric banding round a central grain. Pearls form in pools of saturated water disturbed by dripping water, so that they are commonly found beneath high avens. Individual pearls may be lmm or many centimeters in diameter. Movement of the larger ones may become impossible and they can then become cemented to the pool floor. Some caves contain spectacular displays of cave pearls; in Jackson's Bay Cave, Jamaica, they cover large areas of passage floor behind low gour barriers . 2. Small concretion of calcite or aragonite formed by concentric precipitation around a nucleus . Synonyms: pisolite; pisolith; (French.) perle des cavernes; (German.) Hohlenperlen; (Greek.) speleomargarites; (Italian.) perle di grotta; (Russian.) pescernij zhemcug; (Spanish.) perla de caverna; (Turkish.) magara incisi; (Yugoslavian.) pecinski biseri, jamski biseri.