sedimentary
Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-3.5 (Mohs), Color: Grey to tan (reveals distinctive hexagonal patterns when wet or polished), Luster: Dull to vitreous, Crystal Structure: Hexagonal corallite arrangement, Cleavage: None/Massive, Specific Gravity: 2.7.
- Hardness
- 3-3
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Physical properties
Hardness: 3-3.5 (Mohs), Color: Grey to tan (reveals distinctive hexagonal patterns when wet or polished), Luster: Dull to vitreous, Crystal Structure: Hexagonal corallite arrangement, Cleavage: None/Massive, Specific Gravity: 2.7.
Formation & geological history
Formed through the fossilization of ancient colonial rugose coral (Hexagonaria) during the Devonian period, approximately 350 million years ago, in shallow tropical seas covering present-day Michigan.
Uses & applications
Primarily used for jewelry, lapidary art, paperweights, and as a popular collector's item and souvenir. It is the state stone of Michigan.
Geological facts
The distinctive pattern is the skeletal remains of coral that lived in warm seas. The name 'Petoskey' comes from an Ottawa Indian chief, Pe-to-se-ga, meaning 'rising sun' or 'rays of hope'.
Field identification & locations
Identify in the field by looking for grey-ish stones with faint hexagonal patterns on beaches; the pattern becomes clearly visible when the stone is wet. Found primarily on the shores of Lake Michigan and Lake Huron.
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