fossil

Fossil Coral (Rugose Coral / Horn Coral Cross-Section)

Rugosa (Order) / Calcite (CaCO3)

Hardness: 3 on Mohs scale (calcite replacement); Color: Yellowish-tan to light brown; Luster: Dull, earthy; Structure: Distinctive radial septa radiating from the center outward; Cleavage: Perfect rhombohedral in calcite matrix.

Hardness: 3 on Mohs scale (calcite replacement)
Color: Yellowish-tan to light brown
Luster: Dull, earthy

Identified July 25, 2026More fossil →

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Physical properties

Formation & geological history

Formed during Paleozoic marine environments (Ordovician to Permian periods, roughly 488 to 251 million years ago). The original calcium carbonate skeletal structure of the coral was buried in marine sediments and mineralized over millions of years.

Uses & applications

Primarily collected as geological educational specimens, decorative display items, and lapidary cabochons.

Geological facts

Rugose corals are commonly called 'horn corals' due to their horn-like horn-shaped exterior. They were solitary or colonial marine organisms that went completely extinct during the Permian-Triassic extinction event, the greatest mass extinction in Earth's history.

Field identification & locations

Identify in the field by looking for circular or horn-shaped fossils displaying clear radial septa radiating from a central area. Commonly found in limestone and shale deposits worldwide, especially in North America and Western Europe.

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