sedimentary

Polished septarian nodule slice

Septarian concretion, commonly calcite-filled cracks in a claystone/mudstone matrix (often with aragonite and brown iron oxides)

AI-generated identification · may be incorrect

Typically brown, tan, and gray with polygonal dark crack patterns and a waxy-to-glassy polished luster; hardness about 3–4 for calcite-rich areas, with earthy claystone matrix. Septaria are irregular concretions, not true crystals, and may show calcite cleavage.

Identified September 3, 2026More sedimentary →

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At a glance

Common name: Polished septarian nodule slice
Scientific name: Septarian concretion, commonly calcite-filled cracks in a claystone/mudstone matrix (often with aragonite and brown iron oxides)
Category: sedimentary
Identified: September 3, 2026
Method: Standard

AI Estimated Value

Approximately $10–$40 for a small polished piece; $50–$150+ for larger, vividly patterned 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 mud-rich sediment dries and contracts around a fossil or organic nucleus, producing cracks later filled by calcite or aragonite; many attractive specimens formed during the Cretaceous–Tertiary, roughly 65–50 million years ago.

Uses & applications

Used as decorative stones, cabochons, display specimens, and metaphysical curiosities; softer than most jewelry stones and susceptible to scratching.

Geological facts

The name derives from Latin septum, meaning “partition,” referring to the internal crack network. Polishing exposes the contrasting mineral-filled fractures and concentric concretion layers.

Field identification & locations

Identify it by its flattened nodule shape, brown clay-rich exterior, polygonal internal cracks, and cream or amber vein fillings; common sources include Utah and Madagascar. Avoid acids and prolonged soaking, which can etch calcite.