fossil
Fossilized Coral (Petoskey Stone type)
Hexagonaria percarinata (Fossilized Rugose Coral)
Hardness: 3-4 (calcite) or 6.5-7 (siliceous); Color: Gray, tan, brown with distinct hexagonal patterns; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None
- Hardness
- 3-4 (calcite) or 6
- Color
- Gray, tan, brown with distinct hexagonal patterns
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 3-4 (calcite) or 6.5-7 (siliceous); Color: Gray, tan, brown with distinct hexagonal patterns; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None
Formation & geological history
Formed during the Devonian Period (approx. 350 million years ago) from ancient reef-building coral colonies. The corals were buried by sediment and eventually replaced by minerals like calcite or silica.
Uses & applications
Primarily used for jewelry, decorative carvings, and as a popular collector specimen. Highly valued in lapidary arts when polished to show the internal structure.
Geological facts
The Petoskey stone is the state rock of Michigan. Each 'eye' in the pattern represents an individual coral polyp that once lived in a warm, shallow sea covering current-day North America.
Field identification & locations
Identify by wetting the stone to reveal the hidden hexagonal pattern. Most commonly found on beaches of Lake Michigan and Lake Huron, particularly after storms or ice melts.
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