fossil

Rugose Coral (Horn Coral) Fossil

Order Rugosa (likely Grewingkia or Zaphrentis genus)

AI-generated identification · may be incorrect

Hardness: 3-4 (calcite composition); Color: Gray, tan, or brown; Luster: Dull/earthy; Structure: Distinctive radial septa and external longitudinal ribbing (rugae); Shape: Solitary conical or cornucopia-like shape.

Hardness: 3-4 (calcite composition)
Color: Gray, tan, or brown
Luster: Dull/earthy

Identified July 8, 2026More fossil →

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Physical properties

Formation & geological history

Formed in warm, shallow marine environments during the Paleozoic Era, ranging from the Ordovician to the Permian periods (approx. 488 to 251 million years ago).

Uses & applications

Primarily used for scientific study and educational purposes, hobbyist collecting, and sometimes as decorative garden stones or lapidary material if silicified.

Geological facts

These fossils are often called 'Horn Corals' due to their horn-like shape. Unlike modern corals, many rugose corals were solitary organisms that lived on the seafloor rather than as part of a connected reef system.

Field identification & locations

Identified by the parallel vertical ridges along the exterior and the circular starburst pattern (septa) visible if the end is broken. Very common in the Midwest US (Ohio, Indiana) and other regions with Paleozoic limestone.