A pisolite is a sedimentary rock made of pisoids, which are concretionary grains – typically of calcium carbonate which resemble ooids, but are more than 2 mm in diameter.[1] These grains are approximately spherical and have concentric layers reaching 10 mm in diameter.
Pisoids in the Conococheague limestone (Upper Cambrian) of eastern Pennsylvania
Pisolitic limestone; Itaboraí, Rio de Janeiro, Brazil; pisolith diameters average 1.0 cm
QEMSCAN mineral map of pisoids
The name derives from the Hellenic word for pea. Bauxites, limonites and siderites often have a pisolitic structure.
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