Pisolite

A pisolite is a sedimentary rock made of pisoids, which are concretionary grains – often of calcium carbonate, but sometimes of rarer minerals – which resemble ooids but are always more than 2 mm in diameter. These grains are approximately spherical and have concentric layers reaching 10 mm in diameter.

The name derives from the Hellenic word for pea. Bauxites, limonites and siderites often have a pisolitic structure.