fossil

Fossilized Coral

Rugose Coral (Order Rugosa) or Tabulate Coral

Hardness of 3-4 on the Mohs scale; colors range from gray, brown, and tan to white; vitreous to dull luster; composed primarily of calcium carbonate (calcite or aragonite); distinctive radiating pattern of septa within the corallite structures.

Identified August 4, 2026More fossil →

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Physical properties

Formation & geological history

Formed in ancient shallow marine environments when coral skeletons were buried rapidly in sediment and preserved through permineralization or replacement by silica or calcite, dating predominantly from the Paleozoic Era (Ordovician to Permian periods, roughly 250 to 500 million years ago).

Uses & applications

Used in lapidary arts, wire-wrapping, cabochons for jewelry, decorative display pieces, and as educational or geological collector items.

Geological facts

Fossil corals, particularly Petoskey stones (a specific type of fossilized rugose coral), are the state stones of Michigan and provide invaluable clues about ancient tropical seas and paleoenvironments in regions that are now temperate or arid.

Field identification & locations

Can be identified in the field by looking for distinct honeycomb or star-like patterns of coral calices on weathered limestone or river rocks; commonly found in sedimentary rock exposures, gravel bars, and glacial drift deposits worldwide.

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Fossilized Crinoid Stem in Limestone

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Fossiliferous Limestone

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