fossil

Fossilized Horn Coral

Rugosa

Conical or horn-shaped. Composed mainly of calcite (calcium carbonate). Features vertical lines or ridges (septa) radiating from the center. Hardness typically around 3-4 (Mohs), depending on the preserving minerals. Color is usually grey, tan, or off-white.

Identified April 26, 2026More fossil →

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Physical properties

Formation & geological history

Formed from marine organisms in shallow, warm seas during the Ordovician to Permian periods (approx. 488 to 252 million years ago). The calcium carbonate skeletons were buried in sediment and fossilized.

Uses & applications

Used primarily for geological study, educational purposes, and collected by hobbyists. Sometimes polished for decorative items.

Geological facts

Horn corals are an extinct order of corals. They could grow as solitary individuals or in colonies. Their extinction occurred during the Permian-Triassic extinction event.

Field identification & locations

Easily identified by their horn-like shape and characteristic radial septa. Commonly found in Paleozoic marine sedimentary deposits worldwide, including parts of North America (e.g., Midwest US).