sedimentary
Petoskey Stone
Hexagonaria percarinata
Hardness: 3.0-3.5 (Mohs scale); Color: Gray to brown (dry), mottled hexagonal patterns (wet/polished); Luster: Dull (natural) to Vitreous (polished); Structure: Colonial coral fossils (Hexagonal cells); Composition: Calcite/Limestone.
- Hardness
- 3
- Luster
- Dull (natural) to Vitreous (polished)
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Physical properties
Hardness: 3.0-3.5 (Mohs scale); Color: Gray to brown (dry), mottled hexagonal patterns (wet/polished); Luster: Dull (natural) to Vitreous (polished); Structure: Colonial coral fossils (Hexagonal cells); Composition: Calcite/Limestone.
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from colonial rugose corals in warm, shallow saltwater seas. Glacial action later plucked the stones and spread them across Michigan.
Uses & applications
Used primarily in jewelry making (pendants, cufflinks), decorative paperweights, lapidary arts, and as a popular souvenir/collector's item.
Geological facts
Named after Ottoman Chippewa Chief Petosegay. It is the designated state stone of Michigan. The unique 'six-sided' pattern is only visible when the stone is wet or polished.
Field identification & locations
Identified by the distinct honeycombed or 'star' pattern. Primarily found along the shores of Lake Michigan and Lake Huron, especially near the city of Petoskey. Collectors look for them on beaches after storms.
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