fossil

Fossiliferous Limestone (with Rugose Coral)

Limestone with Tetracoralla (Rugosa) fossil

Hardness: 3 on Mohs scale (calcite matrix). Color: Tan, beige, light brown. Luster: Dull, earthy. Cleavage: Perfect rhombohedral in calcite portions. Specific gravity: ~2.5-2.7. Features a distinct fan-like radiating structure of a rugose (horn) coral at the base.

Hardness: 3 on Mohs scale (calcite matrix)
Color: Tan, beige, light brown
Luster: Dull, earthy

Identified July 26, 2026More fossil →

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Physical properties

Formation & geological history

Formed in shallow, warm marine environments during the Paleozoic Era (Ordovician to Permian periods, roughly 250-480 million years ago) through the accumulation of calcium carbonate skeletal remains of marine organisms.

Uses & applications

Used in geological studies, educational fossil collections, decorative stone, and as an indicator of ancient marine environments.

Geological facts

Rugose corals, often called horn corals due to their horn-like solitary shapes, went extinct during the Permian-Triassic extinction event about 252 million years ago. Their septa (internal radiating walls) are clearly visible in cross-section at the bottom of this specimen.

Field identification & locations

Identified by the distinctive fan-shaped or star-like septal arrangement visible on the cross-section of the fossil, embedded within a reactive biogenic limestone matrix that fizzes with dilute hydrochloric acid. Common in Paleozoic rock formations worldwide.

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