fossil

Fossil Coral

Rugose or Tabulate Coral Fossil (CaCO3 replacement)

Hardness of 3-4 on the Mohs scale (due to calcification/silicification); color ranges from grey, tan, brown to white; luster is dull to vitreous; crystal structure is microcrystalline or trigonal (calcite/quartz replacement); fracture is uneven.

Identified August 3, 2026More fossil →

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Physical properties

Formation & geological history

Formed in ancient shallow marine environments, typically during the Paleozoic era (such as the Devonian or Carboniferous periods), when coral skeletons were buried in sediment and preserved through mineralization or petrifaction.

Uses & applications

Used in lapidary work, jewelry making (cabochons), educational study, and as a collectible specimen.

Geological facts

Fossil corals often show distinctive star-like or honeycomb patterns representing the individual corallites (coral animal homes). Michigan designated a specific fossil coral (Hexagonaria percarinata, or Petoskey stone) as its state stone.

Field identification & locations

Can be identified by the characteristic honeycomb, web, or radiating star patterns visible on the surface. Commonly found in limestone quarries, ancient seabed deposits, and glacial drift.

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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

sedimentary