Where is Septarian Nodule found?
Septarian Nodule (concretions with calcite-filled cracks)
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Open the appSeptarian Nodule occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Septarian Nodule
Madagascar
Known for large, well-formed septarian nodules with prominent calcite infillings, often exhibiting a striking contrast between the dark matrix and yellow calcite.
Utah, USA
Specifically the Tropic Shale Formation, producing septarian nodules with distinctive patterns and often containing aragonite and barite in addition to calcite.
New Zealand
Found in various sedimentary formations, often with a dark gray matrix and yellow calcite infillings.
England
Occurrences in various Jurassic and Cretaceous sedimentary deposits, particularly in coastal areas.
Collecting tips
- Look for Concretions. Septarian nodules are a type of concretion. Search in sedimentary rock outcrops, particularly shales, mudstones, and limestones, for rounded or irregularly shaped masses that stand out from the surrounding rock.
- Exposed Sedimentary Layers. Coastal cliffs, riverbeds, and road cuts exposing marine or lacustrine sedimentary layers are prime locations. Erosion often exposes these harder concretions.
- Break Open Specimens. Many septarian nodules appear as ordinary concretions from the outside. The characteristic internal cracks and mineral infillings are revealed by breaking them open. Always use appropriate safety gear (eye protection, gloves) when breaking rocks.
- Associated Fossils. Since septarian nodules often form around organic nuclei, the presence of fossils in the surrounding rock can be an indicator of potential septarian nodule formation.
Quick Check
- Color:
- Dark gray to brown exterior, yellow to brown calcite interior.
- Luster:
- Dull exterior, vitreous to pearly interior.
- Streak:
- White (for calcite), typically not applicable for the matrix.
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