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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

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.


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Mindat. Includes image.