| 11. | Many gem-quality ammonites are found within siderite concretions.
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| 12. | A narrow conduit leads to a third room containing concretions and eccentrics.
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| 13. | The answer is that the concretion itself is not Ordovician.
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| 14. | Elongate concretions are well known in the Kimmeridge Clay formation of northwest Europe.
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| 15. | The gorge is deep in places, with concretions jutting from the cliffs.
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| 16. | After sulfates cemented the sediments, hematite concretions grew by precipitation from groundwater.
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| 17. | It has been suggested that the round rocks are chert concretions or nodules.
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| 18. | Plinthite concretions are coherent enough to be separated readily from the surrounding soil.
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| 19. | The majority of the hundreds of known specimens come from a single concretion.
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| 20. | The collision of precious abstractions with vulgar concretions is novel for about 90 seconds.
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