Fossiliferous Limestone with Rugose Coral

Physical Properties

Hardness: 3 (on Mohs scale); Color: Gray to brownish-gray; Luster: Dull/Earthy; Structure: Visible radiating septa (lines) in a circular pattern typical of horn corals; Cleavage: None (fragmented).

Formation & Geological History

Formed in warm, shallow marine environments. The specimen contains the fossilized remains of solitary corals that lived during the Paleozoic era, notably from the Ordovician to the Permian periods (approx. 488 to 251 million years ago).

Uses & Applications

Used primarily as educational specimens, collectibles, and as a component of crushed stone in construction where limestone is quarried.

Geological Facts

Commonly known as 'horn corals' because of their cone-like shape. While these corals were once thriving reef-builders, they went extinct during the Great Permian Extinction over 250 million years ago.

Field Identification & Locations

Identify in the field by look for fan-like or radial patterns on the surface of gray sedimentary rocks. They are frequently found in gravel pits, creek beds, or limestone outcrops in the Midwestern United States and Europe.

Identified on: 4/25/2026

Mode: Standard