fossil

Rugose Coral (Horn Coral) Fossil

Order Rugosa (likely Grewingkia or Zaphrentis genus)

AI-generated identification · may be incorrect

Hardness: 3-4 (Calcite), Color: Tan to greyish-white, Luster: Dull to earthy, Structure: Conical or horn-shaped with vertical ridges (septa) visible on the end.

Identified July 19, 2026More fossil →

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Physical properties

Hardness: 3-4 (Calcite), Color: Tan to greyish-white, Luster: Dull to earthy, Structure: Conical or horn-shaped with vertical ridges (septa) visible on the end.

Formation & geological history

Formed in warm, shallow marine environments primarily during the Ordovician through the Permian periods (approx. 450 to 251 million years ago).

Uses & applications

Primarily used as educational specimens, scientific research, and for fossil collecting.

Geological facts

They are called 'Horn Corals' because of their unique shape resembling a bull's horn. Unlike modern corals, many rugose corals were solitary organisms rather than reef-builders.

Field identification & locations

Identify by looking for the horn shape and radial septa (lines) visible in the calcified cup (calice). Commonly found in limestone outcrops and gravel beds in the Midwestern United States.