fossil

Fossilized Rugose Coral in Limestone

Order Rugosa in Sedimentary Matrix (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale), Color: Gray to tan matrix with white/calcified organic patterns, Luster: Dull (earthy), Structure: Tabulate or horn-like internal septa visible in cross-section.

Identified July 9, 2026More fossil →

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Physical properties

Hardness: 3 (Mohs scale), Color: Gray to tan matrix with white/calcified organic patterns, Luster: Dull (earthy), Structure: Tabulate or horn-like internal septa visible in cross-section.

Formation & geological history

Formed in shallow marine environments during the Paleozoic era (Ordovician to Permian periods). These corals lived on the seafloor and were buried by lime mud, eventually lithifying into limestone.

Uses & applications

Educational specimens, museum exhibits, fossil collecting, and decorative lapidary work.

Geological facts

Rugose corals are commonly known as horn corals because of their characteristic shape. They became extinct during the Great Permian Extinction about 251 million years ago.

Field identification & locations

Identify by looking for 'ladder' or 'spoke' patterns in gray sedimentary rock. Commonly found in riverbeds and limestone outcrops in the Midwest USA and Great Lakes regions.