$Polished septarian nodule (Septarian concretion; calcite/aragonite and barite-filled fractures in a carbonate-rich mudstone, commonly with pyrite) — sedimentary$

sedimentary

Polished septarian nodule

Septarian concretion; calcite/aragonite and barite-filled fractures in a carbonate-rich mudstone, commonly with pyrite

AI-generated identification · may be incorrect

Typically hardness 3–4 (calcite-rich areas), locally up to about 6 if barite or silica is present; brown, gray, tan, and golden-yellow with a brecciated, polygonal pattern. Vitreous to waxy luster; irregular internal cavities and fracture fillings, with no consistent crystal cleavage visible in the polished sphere.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when a carbonate-rich mud concretion dries and cracks, then groundwater deposits calcite, aragonite, barite, and sometimes pyrite in the fractures. Many commercial septarians formed during the Cretaceous, roughly 50–100 million years ago.

Uses & applications

Used as decorative polished spheres, lapidary specimens, bookends, and collector pieces; attractive material is occasionally used in jewelry.

Geological facts

The golden metallic-looking patches may be pyrite or golden calcite, while the pale webbing is commonly calcite. The pictured sphere is human-polished but remains a geological specimen.

Field identification & locations

Identify by its rounded nodule form and polygonal vein network, confirmed by acid fizz on exposed calcite (use caution) and pyrite’s metallic brassy color. Common sources include Utah and Madagascar; value is typically $30–$150 for a polished sphere, higher for large, vivid specimens.