fossil

Fossil Coral (Petoskey / Favosites)

Favosites sp. / Hexagonaria sp. (Calcite/Silica pseudomorph)

AI-generated identification · may be incorrect

Hardness 3 (if calcitic) to 7 (if silicified); yellowish-tan to brown; dull to vitreous luster; reveals a honeycomb or radiating septal structure.

Identified September 26, 2026More fossil →

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Physical properties

Hardness 3 (if calcitic) to 7 (if silicified); yellowish-tan to brown; dull to vitreous luster; reveals a honeycomb or radiating septal structure.

Formation & geological history

Formed through the mineral replacement (permineralization) of colonial rugose or tabulate coral skeletons in warm, shallow Paleozoic seas (roughly 350-400 million years ago).

Uses & applications

Prized by lapidaries for polishing, cabochons, decorative carvings, and sought after by fossil collectors.

Geological facts

Tabulate and rugose corals went extinct during the Permian-Triassic extinction event, leaving behind intricate geometric fossils frequently found in ancient limestone beds.

Field identification & locations

Identifiable by distinct honeycomb or tubular pore patterns across the surface, commonly found along riverbeds, lakeshores, and Paleozoic limestone quarries in the Midwest USA.