sedimentary

Polished septarian nodule

Septarian concretion, commonly calcite/aragonite with brown calcite or barite veins in a limestone–clay matrix

AI-generated identification · may be incorrect

Hardness is about 3–4 for calcite-rich material (Mohs 3 for calcite, up to 3.5–4 for aragonite); yellow-tan matrix, dark brown angular veins, waxy to glossy polish, and irregular internal fracturing. Septarian nodules are non-crystalline aggregates rather than single crystals; calcite may show rhombohedral cleavage.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as carbonate-rich concretions in marine mud during the Cretaceous–Tertiary, roughly 50–100 million years ago; shrinkage and cracking during burial allowed later mineral-rich fluids to deposit the veins.

Uses & applications

Primarily sold as a decorative polished specimen or lapidary cabochon; occasionally used in carvings, bookends, and metaphysical collections, but it has little industrial value.

Geological facts

The name derives from Latin septum, meaning partition, referring to the polygonal vein network. The dark veins are often iron-stained calcite, aragonite, or barite rather than true organic material.

Field identification & locations

Identify it by its rounded nodule form, tan/yellow mudstone matrix, and dark branching crack-fill veins; common sources include Utah and Madagascar. Avoid acids and prolonged soaking, which can etch calcite-rich surfaces.