Where is Septarian Nodule found?
Septarian Nodule (Calcite, Aragonite, Limestone/Shale)
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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 producing large, high-quality Septarian nodules with excellent yellow calcite infillings, often referred to as 'Dragon Stone'.
Utah, USA
The 'Moqui Marbles' or 'Navajo Sandstone' concretions, while not strictly septarian, are related. True Septarian nodules are found in various shale and mudstone formations across Utah, particularly in Cretaceous-age deposits.
New Zealand
Known for large, well-formed Septarian nodules, often found in coastal areas where erosion exposes them from sedimentary cliffs.
England
Found in various sedimentary formations, particularly in Jurassic and Cretaceous clays and shales, such as those along the Jurassic Coast.
Collecting tips
- Look in Sedimentary Rocks. Septarian nodules are found embedded in fine-grained sedimentary rocks like shales, mudstones, and limestones. Look for exposed rock faces, riverbeds, or coastal cliffs where these formations are present.
- Identify Concretionary Shapes. Look for rounded to ovoid, sometimes irregular, masses that stand out from the surrounding rock. They are often harder and more resistant to weathering than the host rock.
- Examine Broken Surfaces. If a nodule is broken, the characteristic internal network of cracks filled with contrasting minerals (typically yellow or white calcite) will be visible, confirming its identity as a Septarian nodule.
- Check for Weathering. Septarian nodules often weather out of their host rock due to differential erosion, making them easier to spot as loose specimens on the ground or in stream beds.
Quick Check
- Color:
- Dark grey/brown exterior, yellow/white/brown interior infillings.
- Luster:
- Dull exterior, vitreous to pearly interior.
- Streak:
- White (for calcite/aragonite), streak of matrix varies depending on composition (e.g., grey for shale).
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