sedimentary
Petoskey Stone (Fossilized Coral)
Hexagonaria percarinata
AI-generated identification · may be incorrectHardness: 3-4 (Mohs), Color: gray to tan, Luster: dull to vitreous when polished, Crystal structure: hexagonal patterns of calcite, Specific gravity: approx 2.7
Identified More sedimentary →
Explore Petoskey Stone (Fossilized Coral) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3-4 (Mohs), Color: gray to tan, Luster: dull to vitreous when polished, Crystal structure: hexagonal patterns of calcite, Specific gravity: approx 2.7
Formation & geological history
Formed from fossilized colonial rugose coral living during the Devonian Period (approx. 350 million years ago) in shallow seas, later compressed into limestone and transported by glaciers.
Uses & applications
Commonly used for jewelry (pendants, rings), decorative ornaments, collection, and as the official state stone of Michigan.
Geological facts
The unique 'eye' pattern is the fossilized skeleton of individual coral polyps. The name 'Petoskey' comes from an Ottawa Indian Chief named Petosegay meaning 'beams of rising sun'.
Field identification & locations
Identified by the distinct 6-sided hexagonal patterns visible when wet or polished. Commonly found on the shores of Lake Michigan and Lake Huron. Collectors should look for the honeycomb pattern.
More like this
Other sedimentary specimens
Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion
Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image
fossil
Fossiliferous Sedimentary Rock
Sedimentary limestone with invertebrate fossil imprint
fossil
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite
sedimentary
Shale
Shale (clastic sedimentary rock)
sedimentary
Shale (or Mudstone/Siltstone)
Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)
sedimentary