fossil

Petoskey Stone

Hexagonaria percarinata

Mohs hardness of 3 to 4, distinctive hexagonal coral pattern, dull to subvitreous luster, and calcium carbonate composition.

Identified November 11, 2026More fossil →

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Physical properties

Mohs hardness of 3 to 4, distinctive hexagonal coral pattern, dull to subvitreous luster, and calcium carbonate composition.

Formed during the Devonian period around 350 million years ago through the fossilization of colonial rugose corals.

Used primarily in lapidary arts, decorative carvings, jewelry making, and as a popular collectible item.

It is the official state stone of Michigan and features unique patterns that become much more visible when wet or polished.

Easily identified in the field by its characteristic mosaic of six-sided coral corallites, commonly found along Michigan's northern lake shores.

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image