$Polished septarian pebble (Septarian nodule fragment, typically calcite-filled fractures in a claystone or limestone matrix) — sedimentary$

sedimentary

Polished septarian pebble

Septarian nodule fragment, typically calcite-filled fractures in a claystone or limestone matrix

AI-generated identification · may be incorrect

Dark brown-gray, fine-grained and opaque with contrasting cream calcite veins; polished surface has dull to vitreous luster. Matrix hardness is about Mohs 3–5, while calcite veins are Mohs 3 and show rhombohedral cleavage.

Identified August 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when shrinkage cracks develop in mud-rich sedimentary nodules and later fill with calcite, sometimes aragonite or barite. Commonly Cretaceous to Eocene in age, depending on locality.

Uses & applications

Used as a lapidary stone for cabochons, palm stones, polished slices, and ornaments; rarely used in construction. Value is mainly decorative and collectible.

Geological facts

The cream cross-shaped pattern represents mineral-filled fracture networks, not fossil remains. Acid can weakly fizz on exposed calcite veins, but polishing may obscure the reaction.

Field identification & locations

Identify by its rounded polished form, dark claystone matrix, and angular pale vein network; common sources include Madagascar, Utah, England, and New Zealand. Test cautiously with a steel point and dilute acid on an inconspicuous area.