A septarian nodule is a rounded concretion with internal cavities or cracks filled by minerals such as calcite or aragonite. Look for the distinct cracked, polygonal surface pattern resembling turtle shell or dragon skin. It occurs in sedimentary shale formations and shows best when sliced and polished.
Is this septarian nodule?
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 nodule with a known reference. Septarian Nodule 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 Nodule leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Septarian Nodule 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 Nodule vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside septarian nodule
Minerals reported to co-occur with septarian nodule. 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
Where rockhounds find septarian nodule
6 mapped spotsClassic worldwide localities
- Utah
- Madagascar
- Morocco
- New Zealand
- England
Field-hunting tip
Look in shale country, the host setting where septarian nodule 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
How do you identify septarian nodule?+
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Find septarian nodule on the map
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