Rock Identifier
Fossilized Coral (Rugosa / Scleractinia (Agatized or Calcitized Coral)) — fossil
fossil

Fossilized Coral

Rugosa / Scleractinia (Agatized or Calcitized Coral)

AI-generated identification · may be incorrect

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
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Physical properties

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

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

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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

sedimentary
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Weathered fossil bone fragment (identification uncertain)

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

fossil