Sandstone concretions
Lithogenous and biogenous sedimentary rock.
Sandstone concretions like these typically nucleate on organic remains or shell material. The remains of the creature that they nucleate on may not be preserved (not having a calcareous shell). Tight calcareous or silica cement can form fairly rapidly around a decaying organism before host sediment is compacted with burial. Miocene age, Anza-Borrego desert area, San Diego County, California.
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| https://gotbooks.miracosta.edu/rocks/sedimentary27.html |
2/2/2021 |
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