sedimentary
Fossilized Coral (Petoskey Stone / Chain Coral)
Scleractinia (Order) / Halysites (Genus for Chain Coral types)
Hardness: 3-4 (Mohs scale), Color: White, cream, or light grey, Luster: Dull to earthy, Structure: Hexagonal or colonial tube patterns, Cleavage: None (concretionary/fossilized structure)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: White, cream, or light grey, Luster: Dull to earthy, Structure: Hexagonal or colonial tube patterns, Cleavage: None (concretionary/fossilized structure)
Formation & geological history
Formed through the fossilization of ancient marine invertebrates (polyps) in warm, shallow seas. Over millions of years (commonly Devonian or Silurian periods), calcium carbonate skeletons are replaced by minerals like calcite or silica.
Uses & applications
Used primarily in lapidary work for jewelry, ornaments, and decor. Also used for educational specimens and in construction as a component of limestone.
Geological facts
Fossilized corals are often millions of years older than the mountain ranges where they are now found. They serve as important indicators (paleo-proxies) for ancient climates and sea levels.
Field identification & locations
Identify in the field by looking for repeating geometric or honeycomb patterns on the surface of limestone or light-colored rocks. Usually found in ancient sea beds, river banks, and glacier-tilled areas.
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