Rock Identifier
Fossil Coral (Petoskey Stone / Favosites / Charlevoix Stone) (Hexagonaria percarinata / Favosites (Cnidaria)) — fossil
fossil

Fossil Coral (Petoskey Stone / Favosites / Charlevoix Stone)

Hexagonaria percarinata / Favosites (Cnidaria)

AI-generated identification · may be incorrect

Hardness: 3-4 on Mohs scale (composed mainly of calcite). Color: Gray, tan, and light brown with distinct, repeated cell structures or parallel line patterns. Luster: Dull to earthy in raw form, waxy to vitreous when polished. Structure: Colonial coral skeleton showing corallite structures.

Hardness
3-4 on Mohs scale (composed mainly of calcite)
Luster
Dull to earthy in raw form, waxy to vitreous when polished
Identified More fossil →
Explore Fossil Coral (Petoskey Stone / Favosites / Charlevoix Stone) in the encyclopedia →

Identify your own rocks.

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

App StoreGoogle Play

Physical properties

Hardness: 3-4 on Mohs scale (composed mainly of calcite). Color: Gray, tan, and light brown with distinct, repeated cell structures or parallel line patterns. Luster: Dull to earthy in raw form, waxy to vitreous when polished. Structure: Colonial coral skeleton showing corallite structures.

Formation & geological history

Formed during the Middle Devonian epoch (approx. 350-400 million years ago). Colonial coral organisms grew in warm, shallow prehistoric seas and were gradually replaced by calcium carbonate (calcite) and silica during fossilization.

Uses & applications

Used widely for lapidary work, jewelry (beads, pendants), decorative carvings, paperweights, and as a popular rockhound/fossil collection specimen.

Geological facts

When dry, the fossil patterns can appear faded, but wetting or polishing the surface brings out the intricate honeycomb or repeating corallite structure in striking detail.

Field identification & locations

Look for distinctive repeating geometric, lined, or honeycomb-like patterns embedded in a fine-grained, smooth pebble, common along Great Lakes beaches (especially Michigan) and gravel beds.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

fossil
Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Rounded sedimentary pebble (Likely micritic limestone or calcareous sandstone) — sedimentary

Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

sedimentary
Chert with Fossil Brachiopod (Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion) — sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary