sedimentary

Horn Coral Fossil

Rugosa (extinct order of solitary corals)

Hardness: 3-4 (calcite) or 6.5-7 (if silicified/replaced by chalcedony); Color: Gray, brown, or buff with visible radial septa; Luster: Dull to earthy; Structure: Cone-shaped or cylindrical with a cup-like depression (calice) at the top.

Hardness: 3-4 (calcite) or 6
Color: Gray, brown, or buff with visible radial septa
Luster: Dull to earthy

Identified April 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments during the Paleozoic era (Ordovician to Permian periods, roughly 488 to 251 million years ago). The specimen is the fossilized calcium carbonate skeleton of a solitary coral polyp.

Uses & applications

Primarily used as educational specimens, collector's items, and decorative garden/jewelry stones. In some cases, polished fossilized corals are used in unique lapidary art.

Geological facts

Horn corals are called 'solitary' because they grew as single individuals rather than forming large reefs. They went completely extinct during the Great Permian Extinction event.

Field identification & locations

Identify by looking for a 'horn' shape and radiating lines (septa) on the flat end. They are commonly found in limestone outcrops, creek beds, and gravel pits across North America, particularly in the Midwest and Ohio River Valley.

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