fossil

Horn Coral Fossil

Rugosa (Tetracoralla)

Hardness: 3 (calcite composition); Color: Greyish-brown, tan, or dark grey; Luster: Dull to earthy; Shape: Conical or horn-shaped with visible radiating internal septa lines.

Hardness: 3 (calcite composition)
Color: Greyish-brown, tan, or dark grey
Luster: Dull to earthy

Identified July 26, 2026More fossil →

Explore Horn Coral Fossil in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 3 (calcite composition); Color: Greyish-brown, tan, or dark grey; Luster: Dull to earthy; Shape: Conical or horn-shaped with visible radiating internal septa lines.

Formation & geological history

Formed during the Paleozoic Era (Ordovician to Permian, ~488 to 251 million years ago) in warm, shallow marine environments as calcareous skeletons of solitary coral polyps.

Uses & applications

Educational specimens, private collections, jewelry cabochons, decorative rock gardens.

Geological facts

Rugose corals were marine animals that lived fixed to the seafloor. Unlike modern corals, they grew as solitary 'horns' and became entirely extinct during the Permian-Triassic extinction event.

Field identification & locations

Identified by its distinctive curved cone or horn shape and radiating internal ribs (septa) exposed at the wide end. Commonly found in Paleozoic limestone and shale formations worldwide.