sedimentary
Septarian Nodule
Calcite-infilled Concretion
AI-generated identification · may be incorrectHardness 3-4 on Mohs scale, brown and yellow colors, dull to vitreous luster, amorphous nodular structure with distinct polygonal shrinkage cracks.
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Physical properties
Hardness 3-4 on Mohs scale, brown and yellow colors, dull to vitreous luster, amorphous nodular structure with distinct polygonal shrinkage cracks.
Formation & geological history
Formed in sedimentary mudstone layers during the Cretaceous period through the dehydration and cracking of iron-rich concretion centers, later filled with calcite.
Uses & applications
Used primarily in lapidary arts, decorative spheres, bookends, and as collectible geological specimens.
Geological facts
Septarian nodules are often called dragon stones due to their reptilian pattern of intersecting mineral veins.
Field identification & locations
Identify in the field by their distinctive turtle-shell or mud-ball exterior with protruding calcite ridges; found globally in marine sedimentary shales.
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