fossil

Fossilized Coral (Rugose Coral / Horn Coral)

Rugosa / Scleractinia

Mohs hardness around 3 to 4, color typically off-white, grey, or tan, dull to sub-vitreous luster, often shows distinct septa (radial internal walls) and concentric growth rings or a horn-like tubular structure.

Identified August 2, 2026More fossil →

Explore Fossilized Coral (Rugose Coral / Horn Coral) in the encyclopedia →

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Physical properties

Formation & geological history

Formed in ancient marine environments during the Paleozoic era (ranging from the Ordovician to the Permian, roughly 450 to 250 million years ago), where the calcium carbonate skeleton of marine organisms became permineralized or replaced by minerals like calcite or silica over millions of years.

Uses & applications

Used primarily as educational specimens, in rock and fossil collecting, cut and polished into cabochons for jewelry, or studied for paleoenvironmental reconstructions.

Geological facts

Rugose corals, commonly known as horn corals due to their horn-like shape, were solitary or colonial marine animals that went completely extinct during the Permian-Triassic extinction event.

Field identification & locations

Can be identified in the field by looking for distinctive parallel or radiating fine vertical ridges (septa) and a cup-like or conical shape embedded in limestone or sedimentary matrices. Commonly found in regions with exposed ancient seabed limestone, such as the Midwestern United States, parts of Europe, and the UK.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

sedimentary