sedimentary
Fossilized Rugose Coral (Petoskey Stone precursor)
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (Mohs scale), Color: Tan to grey, Luster: Dull or earthy when unpolished, Crystal structure: Hexagonal or colonial patterns, Cleavage: None, Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Tan to grey, Luster: Dull or earthy when unpolished, Crystal structure: Hexagonal or colonial patterns, Cleavage: None, Specific Gravity: 2.6-2.7
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from the fossilized remains of ancient colonial coral in shallow, warm sea environments.
Uses & applications
Commonly used in jewelry (when polished), decorative stone, and popular amongst fossil collectors and geological enthusiasts.
Geological facts
The distinct hexagonal patterns are the skeletons of individual coral polyps. In Michigan, these are known as Petoskey Stones and were designated as the state stone in 1965.
Field identification & locations
Identify by the unique 'honeycomb' or 'star' patterns visible on the surface. Commonly found on beaches of the Great Lakes, particularly Lake Michigan and Lake Huron.
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