Rock Identifier

fossil

Rugose Coral Fossil

Rugosa (Order) / Horn Coral

AI-generated identification · may be incorrect

Mohs hardness around 3-4 (calcite composition), white to light gray color, dull to vitreous luster, often shows distinct radial septa and a horn-like or cup-shaped structure.

Identified August 3, 2026More fossil →

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Physical properties

Mohs hardness around 3-4 (calcite composition), white to light gray color, dull to vitreous luster, often shows distinct radial septa and a horn-like or cup-shaped structure.

Formation & geological history

Formed during the Paleozoic Era (specifically Ordovician to Permian periods, roughly 450 to 250 million years ago) when ancient marine organisms secreted calcium carbonate skeletons in warm shallow seas.

Uses & applications

Used primarily by fossil collectors, in educational displays, and occasionally in lapidary work or jewelry.

Geological facts

Also commonly known as horn corals due to their horn-like shape, they went extinct during the Permian-Triassic extinction event.

Field identification & locations

Found worldwide in sedimentary limestone deposits, often recognized by their distinctive wrinkled outer wall (rugose) and internal radial symmetry.

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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

Rounded sedimentary pebble (Likely micritic limestone or calcareous sandstone) — sedimentary

Rounded sedimentary pebble

Likely micritic limestone or calcareous sandstone

Chert with Fossil Brachiopod (Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion) — sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion