sedimentary
Petoskey Stone (Fossilized Coral)
Hexagonaria percarinata
Hardness: 3-4 (Mohs scale), Color: Gray bits of calcite with white hexagonal patterns, Luster: Dull to vitreous, Crystal structure: Trigonal (as calcite replacement of coral)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray bits of calcite with white hexagonal patterns, Luster: Dull to vitreous, Crystal structure: Trigonal (as calcite replacement of coral)
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from the fossilized remains of colonial rugose corals in warm, shallow seas.
Uses & applications
Used primarily in jewelry, lapidary arts, 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 name originates from an Ottawa Indian Chief, Pet-O-Sega. The patterns are only visible when the stone is wet or polished.
Field identification & locations
Typically found on beaches along Lake Michigan and Lake Huron. Highly identifiable by the distinctive 'six-sided' or hexagonal cell patterns that resemble a beehive when wet.
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