sedimentary
Fossilized Rugose Coral (Horn Coral)
Order Rugosa
Hardness: 3 (if calcite) to 7 (if silicified); Color: Tan, brownish-grey, or earthy red; Luster: Dull or earthy; Crystal Structure: Amorphous and organic-shaped; Cleavage: None; Specific Gravity: 2.7-3.0
- Hardness
- 3 (if calcite) to 7 (if silicified)
- Color
- Tan, brownish-grey, or earthy red
- Luster
- Dull or earthy
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Physical properties
Hardness: 3 (if calcite) to 7 (if silicified); Color: Tan, brownish-grey, or earthy red; Luster: Dull or earthy; Crystal Structure: Amorphous and organic-shaped; Cleavage: None; Specific Gravity: 2.7-3.0
Formation & geological history
Formed in shallow, warm marine environments during the Paleozoic era (Ordovician to Permian periods). These corals were solitary organisms that became fossilized as sediment replaced their organic structure over millions of years.
Uses & applications
Primarily used as educational specimens, collectibles, and occasionally in jewelry or decorative lapidary arts when well-mineralized.
Geological facts
Rugose corals are known as 'horn corals' due to their characteristic horn-like shape. Unlike modern coral, they lived as solitary individuals rather than in massive colonies and became extinct during the Great Dying at the end of the Permian period.
Field identification & locations
Identified by its conical or horn-like shape and characteristic radial septa (lines) visible on the wider end. Commonly found in limestone outcrops across North America and Europe. Look for segmented ring patterns on the exterior.
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