fossil

Fossilized Rugose Coral

Order Rugosa

Hardness: 3-4 (if limestone/calcite) or 7 (if silicified); Color: Gray, tan, or brown; Luster: Dull to earthy; Internal structure shows characteristic radial partitions (septa).

Hardness: 3-4 (if limestone/calcite) or 7 (if silicified)
Color: Gray, tan, or brown
Luster: Dull to earthy

Identified July 10, 2026More fossil →

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Physical properties

Hardness: 3-4 (if limestone/calcite) or 7 (if silicified); Color: Gray, tan, or brown; Luster: Dull to earthy; Internal structure shows characteristic radial partitions (septa).

Formation & geological history

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

Uses & applications

Scientific study, educational collections, and decorative lapidary work.

Geological facts

Often called 'Horn Corals' because of their solitary cone-like shape, these organisms are extinct ancestors of modern jellyfish and anemone-like creatures.

Field identification & locations

Identify by looking for radial lines (septa) or honeycomb patterns on the surface of water-worn stones. Commonly found in limestone outcrops and riverbeds in the Midwest US and UK.