sedimentary
Fossilized Coral (Honeycomb Coral)
Favosites (extinct genus of tabulate corals), CaCO3 (Calcium Carbonate)
Hardness: 3-4 (Mohs); Color: Tan, brown, or earthy cream-colored; Luster: Dull to earthy; Crystal Structure: Hexagonal or polygonal honeycomb patterns; Cleavage: None (fractures along fossil lines); Specific Gravity: 2.6-2.7.
- Hardness
- 3-4 (Mohs)
- Color
- Tan, brown, or earthy cream-colored
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Tan, brown, or earthy cream-colored; Luster: Dull to earthy; Crystal Structure: Hexagonal or polygonal honeycomb patterns; Cleavage: None (fractures along fossil lines); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the process of permineralization or replacement where coral colonies were buried under marine sediment. These specimens typically date from the Ordovician to the Permian periods (approx. 488 to 251 million years ago) in warm, shallow marine environments.
Uses & applications
Used primarily as decorative garden stones, aquarium ornaments, or scientific specimens. In some cases, polished fossil coral (Agatized coral) is used in jewelry making and as unique cabochons for collectors.
Geological facts
The genus Favosites is often called 'honeycomb coral' because the closely packed polyps resemble a bees' honeycomb. They are known as 'tabulate' corals because of the horizontal internal plates (tabulae) that supported the polyp as it grew upward.
Field identification & locations
Identify in the field by looking for distinct, repeating polygonal or hexagonal chamber patterns on the surface of limestone or shale. These are commonly found in the Great Lakes region of the US (Michigan, Ohio) and in limestone outcrops worldwide. It will bubble/effervesce if touched with a drop of weak acid (vinegar/HCl).
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