fossil

Polished fossil coral (likely agatized coral)

Fossilized coral; commonly silicified Scleractinia or Tabulate coral, composed mainly of microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Brown to tan, glossy polished surface with irregular coral-like cellular or mottled patterns; quartz hardness about 7, vitreous to waxy luster, no obvious cleavage, specific gravity about 2.6. The rounded shape indicates tumbling or natural water abrasion.

Identified September 5, 2026More fossil →

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At a glance

Common name: Polished fossil coral (likely agatized coral)
Scientific name: Fossilized coral; commonly silicified Scleractinia or Tabulate coral, composed mainly of microcrystalline quartz (SiO₂)
Category: fossil
Identified: September 5, 2026
Method: Standard

AI Estimated Value

About $10–$40 for a common polished sphere; $50–$150+ if the coral pattern, size, and polish are especially attractive.

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

Formed when coral colonies were buried and their carbonate skeletons gradually replaced by silica-rich groundwater, commonly during the Paleozoic–Cenozoic eras. It occurs in ancient limestone reefs and siliceous sedimentary deposits.

Uses & applications

Used as a lapidary material for cabochons, spheres, carvings, ornaments, and fossil collections; not typically used structurally.

Geological facts

Polishing can reveal coral corallites or internal growth textures, though this specimen’s pattern is somewhat indistinct and could also represent jasper or silicified limestone.

Field identification & locations

Look for repeated polygonal corallite cells, contrasting silica colors, and conchoidal fracture; acid testing is unreliable if fully silicified. Common sources include Florida, Indonesia, Madagascar, Morocco, and the western United States.