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
Moeraki Boulders
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The Moeraki Boulders are unusually large spherical boulders lying along a stretch of Koekohe Beach on the wave-cut Otago coast of New Zealand between Moeraki and Hampden. They occur scattered either a
Concretion
…beneath the sulfate reduction zone. A spectacular example of boulder septarian concretions, which are as much as 3 meters (9.8 feet) in diameter, are the Moeraki Boulders. These concretions are found eroding out of Paleocene mudstone of the Moeraki Formation exposed along the coast near Moeraki, South Island, New Zealand…
Boulders of varying sphericity broaching the Otago coast
The boulders at sunrise
A cracked boulder displaying its hollow interior