fossil

Agatized fossil shell or shell-like chalcedony

Silicified carbonate fossil; microcrystalline quartz (SiO₂) replacing calcite/aragonite

AI-generated identification · may be incorrect

Hardness about 6.5–7 for the silica, waxy to vitreous luster, translucent gray-white banding, and brown iron-oxide staining. The curved internal structure and layered appearance suggest a silicified shell or gastropod fragment rather than ordinary agate.

Identified September 21, 2026More fossil →

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At a glance

Common name: Agatized fossil shell or shell-like chalcedony
Scientific name: Silicified carbonate fossil; microcrystalline quartz (SiO₂) replacing calcite/aragonite
Category: fossil
Identified: September 21, 2026
Method: Standard

AI Estimated Value

About $5–$30 as an ordinary field specimen; $30–$150 or more if identification, preservation, polish, and provenance are excellent.

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

Silica-rich groundwater gradually replaced the original carbonate shell during diagenesis, preserving its form and growth layers. The host sediment’s geological age cannot be determined from the image; such fossils occur from Paleozoic through Cenozoic rocks.

Uses & applications

Primarily a collectible fossil or lapidary specimen; polished sections may be used as decorative stone or cabochons. It has little industrial value as an isolated piece.

Geological facts

Silicification can preserve fine shell details while changing the material from relatively soft carbonate to quartz. Brown coloration commonly comes from iron oxides deposited during or after replacement.

Field identification & locations

Look for recognizable shell curvature, growth lines, silica-like hardness, and resistance to dilute acid; intact carbonate would fizz, whereas chalcedony generally will not. Common in sedimentary formations worldwide, especially limestone and volcanic-ash-bearing beds.