fossil

Rugose Coral Fossil

Order Rugosa

Hardness varies from 3 to 4 (calcite), color ranges from dark brown to black due to mineralization, vitreous to dull luster, colonial or solitary horn-shaped structure, perfect cleavage in three directions for constituent calcite.

Identified July 31, 2026More fossil →

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Physical properties

Formation & geological history

Formed during the Paleozoic Era (Ordovician to Permian periods, roughly 488 to 251 million years ago) in ancient shallow marine environments where coral animals secreted calcium carbonate skeletons.

Uses & applications

Used primarily as educational specimens, decorative display pieces, in fossil collecting, and occasionally cut and polished for jewelry.

Geological facts

Also commonly known as 'horn coral' due to their distinctive horn-like shape. Unlike modern scleractinian corals, rugose corals had a distinct calcite skeleton and could be solitary or colonial.

Field identification & locations

Easily identified by its horn-like, conical shape and wrinkled outer wall (epitheca). Found worldwide in limestone and marine sedimentary deposits, particularly in North America and Europe.