fossil

Fossil Coral / Petrifed Coral Agate

Silicified Anthozoa (Agatized Coral)

Hardness: 6.5-7 on Mohs scale; Color: Yellow, orange, tan, and grayish silica with distinct honeycomb or ring-like flower patterns; Luster: Waxy to vitreous; Cleavage: None (conchoidal fracture); Specific gravity: ~2.6-2.65

Hardness: 6
Luster: Waxy to vitreous

Identified July 25, 2026More fossil →

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Physical properties

Formation & geological history

Formed when ancient coral reefs (often Paleozoic or Cenozoic) were buried in sediment and replaced over millions of years by silica-rich groundwater, turning the calcareous structure into agate/chalcedony.

Uses & applications

Popular among lapidary artists for slabbing, cabochon cutting, jewelry, display specimens, and gemstone collections.

Geological facts

Agatized coral is Florida's state stone and Georgia's state fossil. The replacement of calcium carbonate by silica preserves the intricate internal structures of individual coral polyps.

Field identification & locations

Identified by the distinct flower-like or cellular ring patterns visible on cut or broken surfaces, along with a high hardness resistant to scratching by steel. Common in sedimentary basins, ancient marine deposits, and limestone regions.

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