fossil

Petrified Coral Fossil

Rugose or Tabulate Coral (Hexagonaria or similar fossilized cnidarian)

Hardness of 3.5 to 4 on the Mohs scale (due to silicification or calcification), colors range from white, grey, to brownish tones, dull to vitreous luster, amorphous to microcrystalline quartz/calcite structure, specific gravity around 2.6-2.7.

Identified July 30, 2026More fossil →

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Physical properties

Formation & geological history

Formed in ancient shallow marine environments during the Paleozoic era (Devonian period, approximately 350-400 million years ago) where coral skeletons were gradually replaced by silica or calcite minerals through permineralization.

Uses & applications

Used primarily as decorative lapidary material, in jewelry making, and highly sought after by fossil collectors.

Geological facts

Many fossilized corals like Petoskey stones are State stones and provide a glimpse into ancient tropical seas that covered areas now far inland, such as the midwestern United States.

Field identification & locations

Easily identified by the distinctive hexagonal or circular honeycomb-like corallite patterns on the surface. Commonly found in gravel beds, glacial drift, and sedimentary limestone formations in regions like the Great Lakes.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

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