fossil

Rugose Coral Fossil (Horn Coral)

Order Rugosa

Hardness: 3-4 (Calcite), Color: Grey, brown, or beige, Luster: Vitreous to dull, Crystal Structure: Trigonal (calcium carbonate replacement)

Identified July 28, 2026More fossil →

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Physical properties

Hardness: 3-4 (Calcite), Color: Grey, brown, or beige, Luster: Vitreous to dull, Crystal Structure: Trigonal (calcium carbonate replacement)

Formation & geological history

Formed from marine organisms that lived primarily during the Paleozoic Era (Ordovician to Permian periods, roughly 488 to 251 million years ago) in shallow tropical marine environments.

Uses & applications

Used in fossil collecting, educational displays, and occasionally polished for ornamental jewelry.

Geological facts

Rugose corals are commonly called 'horn corals' due to their unique horn-like curved shape. They could be solitary or colonial, and the solitary forms are often preserved as individual fossils like the specimen shown.

Field identification & locations

Easily identified by their distinctive horn-like shape and internal radial septa structure. Often found in limestone and shale deposits worldwide, especially in areas with ancient Paleozoic sea beds.