sedimentary

Septarian nodule fragment

Calcite-filled septarian concretion, commonly with a mudstone or limestone matrix

AI-generated identification · may be incorrect

Brown rounded specimen with a network of polygonal cracks and pale mineral infill. Likely calcite and clay-rich matrix; calcite is Mohs 3, with vitreous-to-dull luster and rhombohedral cleavage. Internal structure cannot be confirmed from the photo.

Identified October 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when a sedimentary concretion shrank or cracked during burial, with later mineral-rich fluids filling the fractures. Septarian nodules commonly date from the Cretaceous, though age depends on locality.

Uses & applications

Collected as a geological specimen and sometimes cut or polished for display; larger decorative pieces may be used in lapidary work.

Geological facts

The branching cracks are called septaria; they may be filled by calcite, aragonite, or other minerals.

Field identification & locations

Look for a rounded concretion with angular, branching veins that contrast with its matrix. Septarian nodules occur in sedimentary deposits worldwide, including Utah and Madagascar.