sedimentary

Polished septarian nodule

Septarian concretion, commonly calcite-filled mudstone (calcite CaCO₃, aragonite, barite, and clay minerals)

AI-generated identification · may be incorrect

Hardness is typically 3–4 for calcite-rich areas and about 6–7 for the enclosing matrix; tan-brown exterior with gray, cream, or golden mineral-filled cracks, earthy to waxy luster, and irregular internal cavities. Calcite commonly shows rhombohedral cleavage and may effervesce in dilute hydrochloric acid.

Identified August 23, 2026More sedimentary →

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At a glance

Common name: Polished septarian nodule
Scientific name: Septarian concretion, commonly calcite-filled mudstone (calcite CaCO₃, aragonite, barite, and clay minerals)
Category: sedimentary
Identified: August 23, 2026
Method: Standard

AI Estimated Value

Approximately $20–$100 for a hand-sized polished specimen; exceptional large, colorful, or crystal-lined examples may reach $150–$500.

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 a clay-rich sedimentary nodule contracts and cracks during burial; mineral-rich groundwater later fills the fractures. Many commercial specimens formed in Cretaceous–Eocene marine sediments, roughly 50–100 million years ago.

Uses & applications

Used as decorative polished stone, bookends, cabochons, and metaphysical collectibles; not generally used as structural construction stone.

Geological facts

The characteristic polygonal crack network is called septaria. Golden-brown coloration commonly comes from iron oxides, while gray or sparkling veins are often calcite or aragonite.

Field identification & locations

Identify by its rounded nodule shape, polygonal veins, contrasting clay matrix, and relatively soft calcite fillings; common sources include Utah, Madagascar, Morocco, and England. A polished surface can obscure acid reaction and texture.