sedimentary

Polished septarian nodule

Septarian calcite–aragonite nodule, commonly with chalcedony and iron-oxide minerals

AI-generated identification · may be incorrect

Hardness varies by component: about 3 for calcite, 3.5–4 for aragonite, and up to 7 for chalcedony; polished gray-brown matrix with yellow-orange mineral-filled cracks, vitreous to waxy luster, and no consistent crystal form visible.

Identified August 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when a mud-rich concretion dries and contracts, producing radial cracks later filled by calcite, aragonite, barite, or silica; many commercial examples formed in Cretaceous–Tertiary marine sediments, roughly 65–150 million years old.

Uses & applications

Primarily sold as a decorative sphere, lapidary specimen, and collector’s item; it has little industrial value in this polished form.

Geological facts

The yellow-orange vein material is commonly calcite or aragonite colored by iron oxides. Septarian patterns are sometimes called “dragon stone,” though this is a trade name rather than a formal mineral species.

Field identification & locations

Identify it by its brown mudstone-like matrix and contrasting polygonal crack network, commonly revealed by cutting and polishing; notable sources include Madagascar, Utah, England, and Morocco.