sedimentary
Fossilized Coral (Petoskey Stone or similar Favosites)
Hexagonaria percarinata / Favosites (Silurian-Devonian Coral)
Hardness: 3-4 (Mohs scale), Color: tan, grey, brown with white borders, Luster: dull to waxy when polished, Crystal structure: Hexagonal/calcite-based, Porous texture with visible septa
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Physical properties
Hardness: 3-4 (Mohs scale), Color: tan, grey, brown with white borders, Luster: dull to waxy when polished, Crystal structure: Hexagonal/calcite-based, Porous texture with visible septa
Formation & geological history
Formed during the Devonian or Silurian periods (approx. 350-400 million years ago) from the calcified remains of ancient reef-building coral colonies in warm shallow seas.
Uses & applications
Lapidary use, jewelry making, ornamental stones, and popular as scientific/educational collectibles.
Geological facts
These corals lived during a time when much of North America was covered by tropical seas. After the seas receded, the skeletons fossilized and were later moved by glacial activity.
Field identification & locations
Field identification involves looking for distinct honeycomb or star-like patterns on the surface. They are commonly found on shorelines of the Great Lakes (especially Michigan) and limestone quarries.
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