sedimentary

Horn Coral Fossil

Rugosa (Order Rugosa)

AI-generated identification · may be incorrect

Hardness: 3 (if calcite) to 7 (if silicified); Color: Gray, tan, or white; Luster: Dull to earthy; Structure: Solitary 'horn' shape with internal septa radiating from a center; Cleavage: None (fracture)

Hardness: 3 (if calcite) to 7 (if silicified)
Color: Gray, tan, or white
Luster: Dull to earthy

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the fossilization of marine organisms in shallow sea environments. Most specimens date from the Ordovician to the Permian periods (approx. 488 to 251 million years ago).

Uses & applications

Educational purposes, museum displays, and private geological collections. Rarely used in jewelry as 'fossil coral' cabochons.

Geological facts

Horn corals are extinct. Unlike modern corals, they were solitary organisms that lived on the seafloor. They went extinct during the 'Great Dying' at the end of the Permian period.

Field identification & locations

Identify in the field by the distinct cone shape and the radial pattern (septa) visible on the broken cross-section. Commonly found in limestone outcrops and riverbeds in the Midwest US and UK.