fossil

Fossilized Coral

Hexagonaria (Rugose coral) / Calcium Carbonate (CaCO3)

Hardness of 3-4 on the Mohs scale, colors typically tan, grey, brown, or white, dull to vitreous luster, hexagonal or honeycomb crystal/cellular structure, specific gravity around 2.7.

Identified August 3, 2026More fossil →

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Physical properties

Hardness of 3-4 on the Mohs scale, colors typically tan, grey, brown, or white, dull to vitreous luster, hexagonal or honeycomb crystal/cellular structure, specific gravity around 2.7.

Formation & geological history

Formed during the Devonian period (approximately 350-400 million years ago) when ancient shallow seas covered the region. The coral skeletons were preserved and mineralized through petrifaction, often replaced by silica or calcite.

Uses & applications

Popular as a lapidary material for jewelry, decorative objects, and as a prized specimen for fossil collectors.

Geological facts

Also known as Petoskey stone, it is the state stone of Michigan. The honeycomb pattern represents the corallites (individual coral animals) that lived in colonies millions of years ago.

Field identification & locations

Easily identified in the field or along shores by its distinctive hexagonal or patterned cellular structure resembling a honeycomb. Commonly found in glaciated gravel deposits and limestone formations.

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Fossilized Crinoid Stem in Limestone

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Fossiliferous Limestone

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Fossiliferous Limestone with Crinoid stems

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