fossil
Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (Mohs scale), Color: tan to gray-green (with distinctive hexagon patterns), Luster: dull to earthy (waxy when wet or polished), Structure: hexagonal coral skeletons (calcite)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: tan to gray-green (with distinctive hexagon patterns), Luster: dull to earthy (waxy when wet or polished), Structure: hexagonal coral skeletons (calcite)
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) in shallow, tropical seas. They are fossilized colonial rugose corals mineralized with calcite and eventually glaciated and moved across the Michigan area.
Uses & applications
Used primarily for jewelry making, lapidary art, decorative paperweights, and as a popular souvenir or collector's item in the Great Lakes region.
Geological facts
It is the state stone of Michigan. The name 'Petoskey' comes from an Ottawa Indian Chief, Pet-O-Sega, meaning 'Rising Sun'. The pattern only becomes clearly visible when the stone is wet or polished.
Field identification & locations
Can be identified by the 'honeycomb' or hexagonal pattern on the surface. Commonly found on the beaches of Lake Michigan and Lake Huron. They are most easily spotted when wet, as the pattern 'disappears' when dry and dusty.
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