fossil

Polished fossil coral (likely agatized/tabulate coral)

Fossilized coral, commonly silicified as chalcedony/quartz (SiO₂); exact coral genus cannot be determined from the image

AI-generated identification · may be incorrect

Brown to reddish-brown, translucent to opaque, with glossy polish and elongated parallel coral structures. Silica has Mohs hardness about 6.5–7, vitreous to waxy luster, and no obvious cleavage; specific gravity is approximately 2.6.

Identified September 5, 2026More fossil →

Explore Polished fossil coral (likely agatized/tabulate coral) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Ancient coral colonies were buried and gradually replaced by silica-rich groundwater, preserving skeletal textures; age depends on locality, commonly Paleozoic to Cenozoic. It forms in former shallow marine limestone reefs.

Uses & applications

Used as a cabochon, pendant, bead, or collectible polished fossil; not typically used in construction. Value is primarily decorative and depends on pattern, polish, size, and confirmed provenance.

Geological facts

The apparent ribbed or cellular pattern reflects original coral architecture rather than crystal growth. Acid testing is unreliable because silicified specimens may not fizz, while unsilicified calcitic coral would react strongly.

Field identification & locations

Identify by preserved repeating coral tubes or cells, curved layered pattern, and hardness greater than calcite; common sources include Indonesia, Madagascar, Morocco, and the United States. Estimated value: $10–$60 for a small polished piece, occasionally $100+ for exceptional specimens.