sedimentary
Coral Fossil (Favosites)
Favosites (Calcite/Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale); Color: White, tan, or gray; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71
- Hardness
- 3 (Mohs scale)
- Color
- White, tan, or gray
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: White, tan, or gray; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71
Formation & geological history
Formed through the fossilization of colonial coral polyps in warm, shallow marine environments. Most common specimens date to the Silurian and Devonian periods (approx. 443 to 358 million years ago).
Uses & applications
Primarily used for geological education, museum display, and private collecting. Occasionally used in jewelry (as 'Petoskey stones' when polished) or as decorative garden stone.
Geological facts
Commonly known as 'Honeycomb Coral' due to the hexagonal shape of the individual polyp chambers (corallites). They were reef-builders long before the extinction events that wiped out many prehistoric marine species.
Field identification & locations
Identify by looking for a honeycomb-like pattern of tiny holes or ridges on the surface. Commonly found in limestone quarries and along lake shores in the Great Lakes region (USA). Collectors look for well-defined 'eyes' or chambers.
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