Rock Identifier
Rugose Coral (Horn Coral) Fossil (Order Rugosa (likely Grewingkia or Zaphrentis genus)) — fossil
fossil

Rugose Coral (Horn Coral) Fossil

Order Rugosa (likely Grewingkia or Zaphrentis genus)

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 More fossil →
Explore Rugose Coral (Horn Coral) Fossil in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App StoreGoogle Play

Physical properties

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.

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.

More like this

Other fossil specimens

Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
Sedimentary Outcrop (Sandstone/Shale) (Sedimentary bedrock formation (variable composition)) — sedimentary

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary
Fossiliferous Limestone (Fossiliferous Calcilutite / Biomicrite) — sedimentary

Fossiliferous Limestone

Fossiliferous Calcilutite / Biomicrite

sedimentary
Fossiliferous Limestone (Biogenic Limestone with Brachiopod/Crinoid fragments) — sedimentary

Fossiliferous Limestone

Biogenic Limestone with Brachiopod/Crinoid fragments

sedimentary
Fossilized Crinoid Stem in Limestone (Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix) — fossil

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil
Fossiliferous Limestone (Limestone with embedded fossil cross-section) — sedimentary

Fossiliferous Limestone

Limestone with embedded fossil cross-section

sedimentary