lapillus

A small, solidified fragment of lava.

A small stone; specifically, in the plural, fragmentary materials ejected from volcanoes in eruption, varying in size from that of a pea to that of a walnut. They are sometimes so cellular in structure as to float on the surface of water.

In anatomy, an ear-stone; an otolith; one of the hard concretions found in the fluid of the labyrinth of the ear of many animals. See otolith.