sedimentary
Honeycomb Coral Fossil (Petoskey-type Coral)
Favosites (Extinct Colonial Tabulate Coral), CaCO3
Hardness: 3-4 (Mohs scale), Color: Tan to light gray, Luster: Dull/Earthy, Crystal Structure: Trigonal (as calcite replacement), Cleavage: None (fragmented), Specific Gravity: ~2.7
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Tan to light gray, Luster: Dull/Earthy, Crystal Structure: Trigonal (as calcite replacement), Cleavage: None (fragmented), Specific Gravity: ~2.7
Formation & geological history
Formed through the fossilization of colonial coral reefs during the Devonian Period (approx. 350-410 million years ago) in shallow, warm tropical seas that once covered parts of modern-day North America.
Uses & applications
Used primarily as decorative collector specimens, educational items for paleontology, and occasionally polished for jewelry or lapidary art.
Geological facts
Favosites are known as 'honeycomb corals' because of the polygonal shape of the individual coral cells (corallites). They are an extinct order of coral that vanished during the Permian-Triassic extinction event.
Field identification & locations
Identify by the distinct hexagonal or polygonal pore pattern resembling a wasp nest or honeycomb. To test, apply a drop of vinegar; if it bubbles, it confirms the calcium carbonate composition. Common in the Great Lakes region, particularly Michigan and Ohio.
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