Where is Septarian Nodule found?
Septarian Nodule
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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, high-quality Septarian nodules with excellent yellow calcite infillings, often from Cretaceous marine shales.
Utah, USA
The 'Dragon Stone' Septarian nodules from the Morrison Formation (Jurassic) are famous for their distinctive patterns and often contain aragonite and calcite.
New Zealand
Found in various sedimentary formations, often with dark mudstone exteriors and light calcite interiors.
England
Occur in Jurassic and Cretaceous clay formations, such as the Oxford Clay and Gault Clay.
Canada
Found in various sedimentary basins, including Alberta and British Columbia.
Collecting tips
- Look for Concretions. Septarian nodules are a type of concretion. Search in areas with exposed sedimentary rock layers, especially shales, mudstones, and limestones, where concretions are known to form.
- Examine Weathered Outcrops. Nodules are often harder than the surrounding host rock and may weather out, accumulating at the base of slopes or in stream beds. Look for rounded or ovoid shapes.
- Check for Cracks. While the exterior may appear unremarkable, sometimes faint cracks or a slightly irregular surface can hint at the internal septarian structure. Breaking open a weathered specimen may reveal the internal pattern.
- Safety Precautions. Always obtain permission before collecting on private land. Be aware of unstable slopes and falling rocks in geological outcrops. Wear appropriate safety gear, including eye protection if breaking rocks. Some septarian nodules can contain trace amounts of pyrite, which can oxidize to sulfuric acid if exposed to moisture and air for prolonged periods, though this is generally not a significant hazard for casual handling.
Quick Check
- Color:
- Exterior: Dull gray/brown/black. Interior: Yellow/brown/white crystalline infillings.
- Luster:
- Exterior: Earthy. Interior: Vitreous to resinous.
- Streak:
- White (for calcite infillings); host rock streak varies.
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