fossil
Petoskey Stone
Hexagonaria percarinata
Hardness: 3-3.5 on Mohs scale; Color: Gray to tan, white when dry; Luster: Dull to vitreous when polished; Crystal Structure: Hexagonal coral cells (corallites); Cleavage: None (fossilized structure)
- Hardness
- 3-3
- Color
- Gray to tan, white when dry
- Luster
- Dull to vitreous when polished
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Physical properties
Hardness: 3-3.5 on Mohs scale; Color: Gray to tan, white when dry; Luster: Dull to vitreous when polished; Crystal Structure: Hexagonal coral cells (corallites); Cleavage: None (fossilized structure)
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from fossilized rugose coral colonies in a warm shallow sea covering Michigan. Fossilization involved permineralization by calcite.
Uses & applications
State stone of Michigan, used for jewelry, lapidary arts, home decor, and as a popular souvenir for collectors.
Geological facts
The name comes from Chief Pet-O-Sega of the Ottawa tribe. The distinctive pattern of the coral is only clearly visible when the stone is wet or polished.
Field identification & locations
Recognized by a unique pattern of six-sided cells with radiating lines. Found commonly along the shores of Lake Michigan and Lake Huron. Wet the stone to see the pattern in the field.
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