fossil
Petoskey Stone
Hexagonaria percarinata (Silicified/Calcitic)
Hardness: 3.0-3.5 (Calcite) or 6.5-7.0 (if silicified); Color: Tan, brown, gray; Luster: Waxy to dull (natural) or glassy (polished); Structure: Hexagonal colonial coral pattern.
- Hardness
- 3
- Color
- Tan, brown, gray
- Luster
- Waxy to dull (natural) or glassy (polished)
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Physical properties
Hardness: 3.0-3.5 (Calcite) or 6.5-7.0 (if silicified); Color: Tan, brown, gray; Luster: Waxy to dull (natural) or glassy (polished); Structure: Hexagonal colonial coral pattern.
Formation & geological history
Formed during the Devonian Period (approx. 350-400 million years ago) from colonial rugose corals in shallow, warm seas that once covered Michigan.
Uses & applications
Jewelry, lapidary art, paperweights, souvenirs, and scientific study of prehistoric reefs.
Geological facts
It is the official state stone of Michigan. The name comes from Ottawa Chief Pet-O-Sega. The 'eye' patterns are the individual corallites of the fossilized coral colonial organism.
Field identification & locations
Identified by the distinct six-sided star/honeycomb pattern that becomes highly visible when wet or polished. Commonly found on beaches of Lake Michigan and Lake Huron.
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