sedimentary

Polished fossiliferous agate

Chalcedony (microcrystalline SiO₂), likely containing fossil coral or stromatoporoid structures

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; translucent gray, cream, tan, and reddish-brown bands with waxy to vitreous luster. Fibrous microcrystalline quartz has no obvious cleavage, conchoidal fracture, and specific gravity near 2.6.

Identified August 28, 2026More sedimentary →

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At a glance

Common name: Polished fossiliferous agate
Scientific name: Chalcedony (microcrystalline SiO₂), likely containing fossil coral or stromatoporoid structures
Category: sedimentary
Identified: August 28, 2026
Method: Standard

AI Estimated Value

About $10–$40 for a small common polished specimen; $50–$150 or more for unusually clear, attractive, or diagnostically preserved fossil patterns.

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 filled cavities and replaced porous carbonate fossils, producing chalcedony banding and preservation of internal biological structures. The exact geological age depends on the fossil, commonly Paleozoic to Cenozoic.

Uses & applications

Used as a decorative polished specimen, cabochon, paperweight, or lapidary material; agate is also used for beads and carvings. Fossil-bearing pieces have added collecting interest.

Geological facts

The circular and radiating patterns are consistent with fossil coral or related colonial organisms rather than ordinary banded agate alone. Iron oxides likely create the rusty red coloration.

Field identification & locations

Identify by its waxy translucency, conchoidal fracture, hardness, and repeated fossil-like chambers or corallites; a steel file should generally not scratch it. Common sources include limestone and volcanic terrains worldwide, especially Brazil, Uruguay, Mexico, Madagascar, and the United States.