sedimentary
Petoskey Stone
Hexagonaria percarinata (Fossilized colonial coral)
Hardness: 3.0-3.5 on Mohs scale; Color: Gray to brown, appearing uniform when dry and revealing a distinctive hexagonal pattern when wet; Luster: Dull to sub-vitreous; Structure: Hexagonal colonial skeletal structure; Specific gravity: Approx 2.7.
- Hardness
- 3
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 3.0-3.5 on Mohs scale; Color: Gray to brown, appearing uniform when dry and revealing a distinctive hexagonal pattern when wet; Luster: Dull to sub-vitreous; Structure: Hexagonal colonial skeletal structure; Specific gravity: Approx 2.7.
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from colonial corals that lived in warm, shallow seas. As mountains rose, the sea receded, and the coral beds were buried and fossilized into limestone. Later, glacial action during the Pleistocene epoch plucked them from their bedrock and deposited them across Michigan.
Uses & applications
Used primarily in jewelry (beads, pendants), as decorative items, souvenirs, and highly prized by fossil collectors and lapidary enthusiasts.
Geological facts
It is the official state stone of Michigan. The name comes from an Ottawa Chief, Pet-O-Sega, which means 'Rising Sun' or 'Rays of Hope' because the pattern resembles a sun.
Field identification & locations
Identify by wetting the stone to reveal the six-sided 'honeycomb' pattern. They are most commonly found on the shores of Lake Michigan and Lake Huron, particularly in the Petoskey and Charlevoix areas of Michigan.
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