sedimentary
Petoskey Stone
Hexagonaria percarinata
Hardness: 3-4 (Mohs scale), Color: Gray to brown with distinctive six-sided coral patterns, Luster: Dull to vitreous when polished, Crystal structure: Orthorhombic (as Calcite)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray to brown with distinctive six-sided coral patterns, Luster: Dull to vitreous when polished, Crystal structure: Orthorhombic (as Calcite)
Formation & geological history
Formed during the Devonian period (approx. 350 million years ago) from fossilized rugose corals in a warm shallow sea, later smoothed by glacial action.
Uses & applications
Used primarily for jewelry, decorative carvings, aquarium decor, and as a popular collector's item and state stone of Michigan.
Geological facts
The Petoskey stone is actually a fossilized coral colony. It was named the state stone of Michigan in 1965. The name comes from an Ottawa Chief, Petosegay.
Field identification & locations
Identified by the distinct hexagonal 'eyes' or honeycomb pattern visible when wet. Commonly found along the shores of Lake Michigan and Lake Huron.
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