sedimentary

Fossilized Rugose Coral (Horn Coral)

Rugosa (Order) - often Grewingkia or Zaphrenthis

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite composition); Color: Tan, brown, or gray; Luster: Dull to earthy; Shape: Characteristic conical or horn-shaped structure with septal ridges inside the cup (calice).

Hardness: 3-4 (Calcite composition)
Color: Tan, brown, or gray
Luster: Dull to earthy

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Calcite composition); Color: Tan, brown, or gray; Luster: Dull to earthy; Shape: Characteristic conical or horn-shaped structure with septal ridges inside the cup (calice).

Formation & geological history

Marine sedimentary environments from the Ordovician to the Permian periods (approx. 488 to 251 million years ago). Formed via the calcification of solitary ahermatypic coral polyps in ancient seas.

Uses & applications

Primarily for paleontological study, educational collecting, and occasionally used in jewelry or as decorative pocket stones.

Geological facts

Rugose corals are known as 'horn corals' because of their unique horn-like shape. They went extinct during the Great Permian Extinction, making them an index fossil for Paleozoic strata.

Field identification & locations

Identify by the cone shape and the radial symmetry (septa) visible in the cross-section. Commonly found in limestone outcrops, creek beds, and quarries across the Midwestern United States and UK.