sedimentary

Polished septarian nodule fragment

Septarian concretion; primarily calcite veins in claystone/mudstone, commonly with aragonite and barite

AI-generated identification · may be incorrect

Gray-brown, smoothly polished, fine-grained matrix with distinctive white, polygonal vein networks; calcite is Mohs 3, with vitreous-to-pearly luster and rhombohedral cleavage. The specimen appears rounded and tumbled or cut-polished.

Identified August 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when carbonate-rich mud concretions crack during burial and dehydration, later filling fractures with calcite and other minerals. Most commercially common material formed in Cretaceous marine sediments, roughly 66–145 million years ago.

Uses & applications

Used as a decorative stone, cabochon, pendant, and collecting specimen; softer pieces are unsuitable for heavy-duty construction, though septarian nodules may be cut into slabs and bookends.

Geological facts

The vein pattern resembles lightning or cellular walls, making each nodule unique; yellow-brown crystals lining cavities may be calcite or aragonite.

Field identification & locations

Identify it by the contrasting gray matrix and irregular white vein network; common sources include Utah and Madagascar. Avoid acids and abrasive cleaning because calcite dissolves and scratches readily.