fossil
Coral Fossil / Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (Mohs scale), Color: Gray to tan with white patterns, Luster: Dull to vitreous when wet or polished, Structure: Hexagonal colonial coral pattern, Composition: Calcite and Calcium Carbonate.
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray to tan with white patterns, Luster: Dull to vitreous when wet or polished, Structure: Hexagonal colonial coral pattern, Composition: Calcite and Calcium Carbonate.
Formation & geological history
Formed during the Devonian Period (approx. 350-400 million years ago) in shallow, tropical seas. Over time, the living coral was buried and replaced by minerals, primarily calcite.
Uses & applications
Commonly used in jewelry (pendants, rings), decorative ornaments, and as a popular collector's item in the Great Lakes region.
Geological facts
The Petoskey Stone is the official state stone of Michigan. The unique 'six-sided star' pattern only reveals itself clearly when the stone is wet or polished.
Field identification & locations
Look for a hexagonal honeycomb-like pattern on the surface, especially when the stone is submerged in water or licked (!). They are most commonly found on the beaches of Lake Michigan and Lake Huron.
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