sedimentary

Polished septarian nodule

Septarian concretion (calcite-filled mudstone, commonly with aragonite and barite)

AI-generated identification · may be incorrect

Typically brown to gray mudstone with cream-to-golden calcite vein fillings and a polished or waxy luster; hardness about 3–4 for calcite-rich areas and up to 6–7 in silica-bearing portions. Irregular septarian crack patterns and contrasting mineral veins are diagnostic;…

Identified August 30, 2026More sedimentary →

Explore Polished septarian nodule in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when shrinkage cracks develop in a carbonate-rich mud concretion and later fill with calcite or aragonite, sometimes barite or quartz. Many commercial specimens formed in Cretaceous–Eocene marine sediments, roughly 50–100 million years ago.

Uses & applications

Used as lapidary material for cabochons, palm stones, spheres, and decorative objects; not generally used structurally.

Geological facts

The name derives from Latin septum, meaning “partition,” referring to the polygonal internal cracks. The photographed piece appears polished and may be a cut fragment rather than a complete nodule.

Field identification & locations

Identify by hard brown matrix intersected by pale mineral veins, irregular cavities, and strong color contrast; common sources include Madagascar, Utah, England, and Morocco. Vinegar may weakly fizz on exposed calcite.