Concretion
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A concretion is a hard and compact mass formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or sphe
Concretions in Torysh, Western Kazakhstan
Concretions with lenticular shapes from an island in the Vltava river, Prague, Czech Republic
Marlstone aggregate concretion, Sault Ste. Marie, Michigan, United States
Concretion rock with white core from the Middle Jurassic of Iran