sedimentary

Polished/tumbled septarian nodule (likely)

Calcite–aragonite–barite septarian concretion; composition varies, commonly calcite (CaCO₃) with clay/mudstone and iron oxides

AI-generated identification · may be incorrect

Rounded, polished dark gray-brown stone with mustard-yellow mineral-filled fractures. Hardness is approximately 3 for calcite-filled areas and 4–6 for the surrounding matrix; earthy to waxy luster, microcrystalline structure, and no obvious cleavage on the polished surface.

Identified August 10, 2026More sedimentary →

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At a glance

Common name: Polished/tumbled septarian nodule (likely)
Scientific name: Calcite–aragonite–barite septarian concretion; composition varies, commonly calcite (CaCO₃) with clay/mudstone and iron oxides
Category: sedimentary
Identified: August 10, 2026
Method: Standard

AI Estimated Value

About $10–$40 for a common polished palm stone; $50–$200+ for large, vividly patterned, or locality-labeled specimens.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Forms when shrinkage cracks develop in a carbonate-rich mud concretion and later fill with calcite, aragonite, barite, or iron minerals. Septarian nodules commonly formed in marine sediments during the Cretaceous–Paleogene, though age depends on locality.

Uses & applications

Used as a lapidary stone, paperweight, cabochon, ornament, and collector specimen; generally unsuitable for structural construction.

Geological facts

The characteristic yellow-brown coloration usually comes from limonite or other iron oxides. Acid may fizz on exposed calcite, and a streak or scratch test can help distinguish it from jasper or slag.

Field identification & locations

Commonly found in Utah and Madagascar, as well as parts of England, Morocco, and the Gulf Coast. Look for angular fracture networks, contrasting calcite veins, and a natural nodule texture; exact identification requires testing or a fresh surface.