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