sedimentary

Polished septarian nodule

Septarian limestone/concretion, typically calcite-filled cracks in a calcite–aragonite–clay matrix

AI-generated identification · may be incorrect

The specimen is polished and oval, with a brown matrix crossed by pale, branching veins. Septarian material is commonly dominated by calcite; hardness varies, roughly 3–4 Mohs, with a dull to waxy matrix and glassy vein surfaces. Exact composition cannot be confirmed from the image.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when cracks developed in a carbonate-rich concretion and were later filled by minerals, often calcite. Many well-known examples formed in Cretaceous marine sediments, though age depends on locality.

Uses & applications

Polished pieces are used for display and lapidary crafts; larger septarian nodules are cut into spheres, slabs, and decorative objects.

Geological facts

The pale branching pattern records mineral-filled fractures, sometimes called septaria. The pictured surface appears polished rather than naturally weathered.

Field identification & locations

Look for a brown or gray concretion with angular or branching contrasting veins; common sources include Utah, Madagascar, and parts of Europe. A hardness test or acid reaction on an inconspicuous spot can help assess calcite, but may damage the polish.