sedimentary
Petoskey Stone
Hexagonaria percarinata
Hardness: 3.0-3.5 (Mohs); Color: Gray to tan when dry, distinct hexagonal pattern appears when wet; Luster: Dull to vitreous when polished; Crystal structure: Orthorhombic (calcite); Specific gravity: Approx 2.7
- Hardness
- 3
- Luster
- Dull to vitreous when polished
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Physical properties
Hardness: 3.0-3.5 (Mohs); Color: Gray to tan when dry, distinct hexagonal pattern appears when wet; Luster: Dull to vitreous when polished; Crystal structure: Orthorhombic (calcite); Specific gravity: Approx 2.7
Formation & geological history
Formed by the fossilization of colonial rugose coral during the Devonian Period (approx. 350 million years ago) in warm, shallow saltwater seas covering Michigan.
Uses & applications
Commonly used in jewelry, lapidary art, decorative paperweights, and as a popular souvenir/collector's item.
Geological facts
The Petoskey stone is the state stone of Michigan. The name comes from an Ottawa Chief named Petosegay, which means 'rising sun' or 'rays of dawn'.
Field identification & locations
Identified by its distinctive 'honeycomb' or hexagonal pattern. Found primarily on the shores of Lake Michigan and Lake Huron. Collectors often use water to reveal the pattern on rough stones.
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