fossil

Agatized Fossil Coral

SiO2 replacing Anthozoa

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Various (brown, tan, grey, white in this specimen), Luster: Vitreous to waxy, Crystal structure: Microcrystalline (chalcedony), Cleavage: None

Hardness: 6

Identified August 25, 2026More fossil →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Various (brown, tan, grey, white in this specimen), Luster: Vitreous to waxy, Crystal structure: Microcrystalline (chalcedony), Cleavage: None

Formation & geological history

Formed when ancient coral was buried in sediment and silica-rich groundwater gradually replaced the calcium carbonate of the coral skeleton with agate/chalcedony. Typically dates to the Oligocene or Miocene epochs (20-30 million years ago).

Uses & applications

Commonly collected by rockhounds, tumbled, cut into cabochons for jewelry, or kept as natural specimens.

Geological facts

The intricate patterns visible are the preserved structural details of the original coral polyps. Florida and Indonesia are famous for producing high-quality agatized coral.

Field identification & locations

Identified by the characteristic honeycomb, star, or tubular patterns of the coral structure preserved within hard, translucent to opaque silica. Found in ancient marine deposits. Tips for collectors: Look for pieces that are solid enough to take a polish, as some may be crumbly or heavily weathered.