Peastone, a carbonate of lime, slightly colored by the oxyd of iron. It occurs in little globular concretions of the size of a pea or larger, which usually contain each a grain of sand as a nucleus. These concretions in union sometimes compose entire beds of secondary mountains. It is sometimes called calcarious tufa.

A variety of calcite, or calcium carbonate, consisting of aggregated globular concretions about the size of a pea; -- called also peastone, peagrit.