fossil

Fossilized Rugose Coral

Order Rugosa

Hardness: 3-4 (Calcite-based), Color: Tans, grays, and creams, Luster: Dull to earthy, Structure: Cylindrical or horn-shaped with radiating internal septa (vertical ridges).

Identified July 2, 2026More fossil →

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Physical properties

Hardness: 3-4 (Calcite-based), Color: Tans, grays, and creams, Luster: Dull to earthy, Structure: Cylindrical or horn-shaped with radiating internal septa (vertical ridges).

Formation & geological history

Formed in warm, shallow marine environments from the Ordovician to the Permian periods (approx. 488 to 251 million years ago) through the permineralization of coral skeletons.

Uses & applications

Used primarily for scientific study, educational collections, lapidary work (when petrified in silica), and as decorative display pieces.

Geological facts

Often called 'Horn Corals' due to their distinctive shape; unlike modern corals, they were frequently solitary rather than colonial. They went extinct during the Great Permian Extinction.

Field identification & locations

Identify by the presence of 'septa' (distinct radiating lines) inside a cone-like structure. Commonly found in limestone beds in the Midwest USA and around the Great Lakes.