Where is Septarian Nodule found?
Septarian Nodule (composed of calcite, aragonite, and chalcedony/quartz within a mudstone or shale matrix)
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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 striking yellow calcite and dark brown matrix, often from Jurassic-age marine shales.
Utah, USA
The 'Dragon Stone' Septarian nodules from the Cretaceous-age Mancos Shale are famous for their intricate patterns of yellow calcite, brown aragonite, and dark gray matrix.
New Zealand
Found in various sedimentary formations, often exhibiting unique internal structures.
Morocco
Produces Septarian nodules, sometimes with distinctive mineral infillings.
United Kingdom
Occurrences in various sedimentary basins, particularly in Jurassic and Cretaceous deposits.
Collecting tips
- Look in Sedimentary Outcrops. Septarian nodules are found in sedimentary rock formations, especially mudstones, shales, and marls. Look for eroded areas where the nodules may have weathered out of the softer host rock.
- Identify Concretionary Shapes. Search for spherical to ovoid, often somewhat flattened, rock masses that stand out from the surrounding bedrock due to their harder composition.
- Check for Weathered Surfaces. The exterior of a Septarian nodule may show faint cracks or a slightly different texture than the host rock. Sometimes, the mineral infillings are visible on weathered surfaces.
- Break Open Suspect Nodules. The definitive identification often requires breaking open a nodule to reveal the characteristic internal septa filled with calcite, aragonite, or chalcedony/quartz.
Quick Check
- Color:
- Exterior: Earthy brown/gray. Interior: Dark matrix with yellow/white/amber veins.
- Luster:
- Exterior: Dull/Earthy. Interior: Vitreous to waxy.
- Streak:
- White (for calcite/aragonite components); the matrix will have a streak similar to mudstone/shale (often gray to brown).
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