What is "gastrolith"

Gastrolith \Gas`tro*lith\, n. [Gastro- + -lith.] (Zo["o]l.) See Crab's eyes, under Crab.

n. (context zoology English) rocks which are or have been held inside the digestive tract of an animal to aid in buoyancy or food processing.

A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In other species the rocks are ingested and pass through the digestive system and are frequently replaced. The grain size depends upon the size of the animal and the gastrolith's role in digestion. Other species use gastroliths as ballast. Particles ranging in size from sand to cobbles have been documented.