Septarian nodule.
Septarian nodules are concretionary masses that have an internal cavity filled in with crystal masses (similar to a geode). They are usually filled with carbonate minerals (calcite, aragonite, siderite) and other minerals that fill in a network of cracks within a rind of dense argillaceous limestone.
This is an example of a septarian nodule from a famous locality in southern Utah where septarian nodules (concretions) occur in marine shales of the Cedar Mountain Formation of Cretaceous age. |
| https://gotbooks.miracosta.edu/rocks/sedimentary/38.html |
2/2/2021 |
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