fossil

Fossil Coral

Hexagonaria or similar rugose/tabulate coral fossil (Calcium Carbonate, CaCO3)

Hardness of 3-4 on the Mohs scale; colors typically range from tan, brown, grey to white; luster is dull to vitreous; hexagonal or circular corallite structures preserved in calcium carbonate or silica replacement.

Identified August 3, 2026More fossil →

Explore Fossil 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

Formed when ancient coral reefs were buried under marine sediments and the original skeletal structures were fossilized through petrifaction or mineral replacement, often dating back to the Devonian period (around 350-400 million years ago).

Uses & applications

Used primarily as a decorative stone, in lapidary arts for cabochons and jewelry, and as a prized specimen for fossil collectors.

Geological facts

Fossil coral is the state stone of Michigan, where the specific species known as Petoskey stone is famously found along the shores of Lake Michigan.

Field identification & locations

Easily identified in the field by its distinct honeycomb or web-like pattern of corallites on the weathered surface; commonly found in ancient limestone deposits and glacial gravels.

Other fossil specimens

See all

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil

Fossiliferous Limestone

Limestone with embedded fossil cross-section

sedimentary

Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

sedimentary