Septarian nodules are rounded concretions that feature internal cavities or cracks filled with minerals like calcite or aragonite. Collectors look for the distinct cracked, polygonal patterns on the surface that resemble a turtle shell or dragon skin. They are typically found in sedimentary shale formations and are best displayed when sliced and polished.
Is this septarian nodules?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch septarian nodules with a known reference. Septarian Nodules sits at Mohs 3-5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Septarian Nodules leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Septarian Nodules typically shows a dull to vitreous luster.
- 4Match the color rangeCompare against the expected color range: brown, yellow, gray, white.
- 5Look at form & habitTypical habit: nodular.
Often confused with
Septarian Nodules vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside septarian nodules
Minerals reported to co-occur with septarian nodules. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-5
- Density
- 2.6-2.9 g/cm³
- Streak
- White
- Luster
- Dull to Vitreous
- Transparency
- Opaque
- Crystal habit
- Nodular
- Cleavage
- None
- Fluorescence
- Often Fluorescent Under SW UV
- Rarity
- Common
- Uses
- Lapidary, Decorative, Collector
- Host rock
- Shale
- Typical price
- $10-100 per specimen
Where rockhounds find septarian nodules
6 mapped spotsClassic worldwide localities
- Utah
- Madagascar
- Morocco
- New Zealand
- England
Field-hunting tip
Look in shale country — that is the host setting where septarian nodules typically forms. If you start seeing calcite, aragonite, barite in float, you are in the right ground. Field specimens usually show a nodular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Kansas, Missouri, Arizona — start trip planning there.
Common questions
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Find septarian nodules on the map
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