sedimentary
Rugose Coral (Horn Coral)
Order Rugosa (extinct fossilized coral)
Hardness: 3-4 (calcite); Color: Tan, brown, or orange due to mineral staining; Luster: Dull to earthy; Shape: Characteristic conical, horn-like shape with septa (ridges) inside the cup.
- Hardness
- 3-4 (calcite)
- Color
- Tan, brown, or orange due to mineral staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (calcite); Color: Tan, brown, or orange due to mineral staining; Luster: Dull to earthy; Shape: Characteristic conical, horn-like shape with septa (ridges) inside the cup.
Formation & geological history
Formed as the calcium carbonate skeleton of a solitary marine polyp. Most common specimens date from the Ordovician to the Permian periods (approx. 488 to 251 million years ago). They lived on the seafloor in ancient tropical seas.
Uses & applications
Primarily used for geological education, fossil collecting, and occasionally as decorative pieces or jewelry components when polished.
Geological facts
Horn corals are extinct; they disappeared during the Great Permian Extinction. Unlike modern corals, many were solitary individuals rather than part of a colonial reef.
Field identification & locations
Identify by its curved, conical shape resembling a bull's horn and the radial symmetry visible in the cross-section of the 'top' or cup. Found globally in limestone and shale deposits.
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