fossil

Fossilized Coral

Rugosa / Scleractinia (Agatized or Calcitized Coral)

Hardness: 3.5 to 7 depending on replacement mineral (calcite vs quartz/agate), Color: White, grey, brownish, or multicolored, Luster: Vitreous to dull, Crystal structure: Hexagonal or amorphous due to replacement, Cleavage: None

Hardness: 3

Identified July 30, 2026More fossil →

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Physical properties

Formation & geological history

Formed when ancient coral skeletons are buried in marine sediments and preserved through permineralization, where minerals like silica or calcite replace the original organic structure over millions of years (Paleozoic to Cenozoic eras).

Uses & applications

Used in ornamental carvings, jewelry, lapidary art, and as educational or geological collector specimens.

Geological facts

Fossil coral often showcases intricate honeycomb or star-like patterns corresponding to the original coral polyps. It is the state stone of Michigan (Petoskey stone).

Field identification & locations

Found in ancient limestone deposits and sedimentary rock layers worldwide, particularly in areas once covered by shallow prehistoric seas. Identify by its distinct cellular coral calicles pattern.

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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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