sedimentary

Petrified Rugose Coral (Horn Coral)

Order Rugosa (extinct coral)

AI-generated identification · may be incorrect

Hardness: 3-4 (if calcite) to 7 (if silicified); Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Conical or horn-shaped with radial septa (internal lines); Cleavage: None (conchoidal fracture if agatized)

Hardness: 3-4 (if calcite) to 7 (if silicified)
Color: Tan, beige, brown
Luster: Waxy to dull

Identified June 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in warm, shallow marine environments. Most common specimens date from the Ordovician to the Permian periods (approx. 488 to 251 million years ago). The organic material was replaced by minerals like calcite or silica over millions of years through permineralization.

Uses & applications

Primarily used as educational specimens, decorative items, and lapidary material for jewelry if agatized (silicified).

Geological facts

Rugose corals are called 'horn corals' due to their resemblance to a bull's horn. They were solitary organisms that lived on the seafloor but became extinct during the Great Permian Extinction.

Field identification & locations

Identify by looking for a cone or horn shape and radial structural lines (septa) visible on the cross-sections. Commonly found in limestone outcrops, riverbeds, and gravel pits across North America and Europe.