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Geodes and Septarian Nodules
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Photo courtesy Kent Simonsen, all rights reserved
are openings that grow within shaly rocks during the process of consolidation. Often they are lined with mineral crystals or smooth, milky layers of chalcedony. Septarian nodules
also have crystalline matter inside them, they send out cracks as they grow and may not have an opening in their centers. Water-worn examples may look like turtle shells or weird sea creatures, but they are not fossils.