Rock Identifier
Petoskey Stone / Rugose Coral Fossil (Hexagonaria percarinata) — fossil
fossil

Petoskey Stone / Rugose Coral Fossil

Hexagonaria percarinata

Hardness of 3 on the Mohs scale, colors range from grey to white when dry and darken to brownish-yellow when wet, dull to waxy luster, hexagonal or corallite structure made of calcium carbonate.

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Physical properties

Hardness of 3 on the Mohs scale, colors range from grey to white when dry and darken to brownish-yellow when wet, dull to waxy luster, hexagonal or corallite structure made of calcium carbonate.

Formation & geological history

Formed during the Devonian period, approximately 350 million years ago, through the fossilization of colonial rugose corals that lived in shallow warm seas.

Uses & applications

Used primarily in lapidary arts, jewelry making, ornamental carvings, and as a popular collectible specimen.

Geological facts

The Petoskey stone is the official state stone of Michigan. The distinctive pattern resembles the sunbursts or honeycomb eyes of ancient coral animals.

Field identification & locations

Easily identified by the characteristic six-sided corallites visible on the surface. Commonly found along the shores of Lake Michigan and Lake Huron, as well as glacial drift deposits in the northern US.

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