sedimentary
Petoskey Stone
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3.0 to 3.5 (Mohs scale); Color: Gray to beige/tan; Luster: Dull/earthy when dry, silky/lustrous when polished; Structure: Hexagonal honeycombed pattern of individual corallites; Cleavage: None (fractures irregularly).
- Hardness
- 3
- Color
- Gray to beige/tan
- Luster
- Dull/earthy when dry, silky/lustrous when polished
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Physical properties
Hardness: 3.0 to 3.5 (Mohs scale); Color: Gray to beige/tan; Luster: Dull/earthy when dry, silky/lustrous when polished; Structure: Hexagonal honeycombed pattern of individual corallites; Cleavage: None (fractures irregularly).
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago). These are fossilized coral colonies that were eventually turned into limestone and then moved by glacial activity during the Pleistocene epoch.
Uses & applications
Primarily used as decorative display pieces, for jewelry (pendants and beads), and as a popular souvenir/collectible.
Geological facts
It is the official state stone of Michigan. The name 'Petoskey' comes from an Ottawa Indian Chief named Pet-O-Sega, meaning 'Rising Sun' or 'Rays of Hope'.
Field identification & locations
Identify in the field by looking for the distinct 'six-sided' or hexagonal snowflake pattern, which is most visible when the stone is wet. Commonly found on the beaches of Lake Michigan and Lake Huron.
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