Rock Identifier

fossil

Rugose Coral Fossil

Order Rugosa

AI-generated identification · may be incorrect

Mohs hardness of 3-4 (calcite), color ranges from grey to tan and brown, displays a distinctive horn-like shape with visible septal structures and radial symmetry.

Identified October 18, 2026More fossil →

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Physical properties

Mohs hardness of 3-4 (calcite), color ranges from grey to tan and brown, displays a distinctive horn-like shape with visible septal structures and radial symmetry.

Formation & geological history

Formed during the Paleozoic era (Ordovician to Permian) when marine organisms secreted calcium carbonate skeletons in ancient shallow seas.

Uses & applications

Used primarily as educational specimens, decorative display pieces, and for biostratigraphic correlation by geologists.

Geological facts

Also known as horn corals due to their curved, horn-like external shape. They went extinct during the Permian-Triassic extinction event.

Field identification & locations

Identify by the distinctive internal septae resembling wheel spokes and the wrinkled outer wall. Commonly found in limestone deposits worldwide.

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

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

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

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

Porous limestone pebble

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

Fossil oyster shell (Oyster (family Ostreidae); shell composed chiefly of calcite (CaCO₃)) — fossil

Fossil oyster shell

Oyster (family Ostreidae); shell composed chiefly of calcite (CaCO₃)