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pisolith (adj. pisolitic) (pisoid) A spherical to subspherical, inorganic carbonate particle, larger than 2 μm in diameter, and in some cases as much as 10 cm in diameter, characterized by an internal concentric lamination. Some pisoliths are said to form in the same manner as ooids, but others (‘vadose pisoliths’), form in subaerial environments in calcrete profiles, Pisoliths should not be confused with oncoids (oncolites) which although superficially similar, are of organic origin.