Where is Septarian Nodule found?
Septarian Nodule (calcite, aragonite, and/or barite veins within a concretion)
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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 prominent yellow calcite veins and dark brown aragonite or mudstone matrix. These are often referred to as 'Dragon Stone'.
Utah, USA
The 'Moqui Marbles' or 'Navajo Cherries' are a type of iron-rich concretion, some of which exhibit septarian features. The Cretaceous Tropic Shale formation is a notable source of septarian nodules.
New Zealand
Found in various sedimentary formations, often with distinctive patterns and colors.
England
Occurrences in Cretaceous chalk and clay formations, particularly in areas like the Isle of Sheppey, Kent, where they are known as 'Sheppey Septaria'.
Canada
Found in sedimentary basins, particularly in Alberta and other western provinces.
Collecting tips
- Look in Sedimentary Outcrops. Focus on areas with exposed marine shales, mudstones, and marls, especially those of Cretaceous age. Septarian nodules often weather out of the softer host rock and can be found loose on the surface or embedded in cliffs.
- Identify Concretionary Shapes. Look for rounded, ovoid, or irregularly shaped masses that are harder and more resistant to weathering than the surrounding rock. The exterior may be rough or bumpy.
- Check for Internal Cracks. If a nodule is broken, look for the characteristic internal network of cracks filled with contrasting mineral veins (typically yellow, white, or brown calcite, aragonite, or barite). This is the definitive feature of a septarian nodule.
- Examine Weathered Surfaces. Sometimes, the infilling minerals are more resistant to weathering than the host rock, causing them to stand out in relief on the nodule's surface, indicating the internal septarian structure.
- Tools for Collection. A rock hammer and chisel may be useful for extracting embedded nodules. Always wear appropriate safety gear, including eye protection.
Quick Check
- Color:
- Exterior: Grey, brown, black. Interior: Dark matrix with lighter veins (yellow, white, brown).
- Luster:
- Dull to vitreous.
- Streak:
- White (for calcite/aragonite veins), white to pale yellow (for barite veins), or grey/brown (for host rock).
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