fossil

Fossil Coral

Rugose coral / Tabulate coral (Phylum Cnidaria)

Hardness: 3-4 (calcite); Color: Gray, white, beige, brown; Luster: Vitreous to dull; Crystal structure: Trigonal (calcite replacement); Cleavage: Perfect rhombohedral in calcite; Specific Gravity: 2.71

Hardness: 3-4 (calcite)
Color: Gray, white, beige, brown
Luster: Vitreous to dull

Identified July 30, 2026More fossil →

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Physical properties

Formation & geological history

Formed in ancient shallow marine environments when coral skeletons were buried in sediment and fossilized through permineralization, commonly replacing original aragonite with silica or calcite, dating from the Paleozoic Era (Ordovician to Permian periods, roughly 250 to 500 million years ago).

Uses & applications

Used in lapidary arts, decorative cabochons for jewelry, educational specimens, and fossil collecting.

Geological facts

Many fossil corals found in North America and Europe are rugose corals, often called 'horn corals' due to their distinctive horn-like shape. Over millions of years, groundwater rich in minerals replaces the original skeletal material, preserving the intricate internal septa and coral structure.

Field identification & locations

Identify by distinct radiating radial patterns (septa) or honeycomb-like coral structures on weathered limestone surfaces. Commonly found in limestone quarries, ancient marine deposits, and riverbeds worldwide.

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Fossiliferous Limestone with Crinoid stems

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