fossil

Horn Coral Fossil

Rugosa (Order Rugosa)

Hardness: 3 on Mohs scale (calcite composition), Color: Gray, beige, and white, Luster: Dull to earthy, Crystal structure: Trigonal (calcite replacement), Specific gravity: 2.7

Identified August 2, 2026More fossil →

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Physical properties

Hardness: 3 on Mohs scale (calcite composition), Color: Gray, beige, and white, Luster: Dull to earthy, Crystal structure: Trigonal (calcite replacement), Specific gravity: 2.7

Formation & geological history

Formed from marine organisms that lived in shallow Paleozoic seas, primarily during the Ordovician to Permian periods (approximately 450 to 250 million years ago). The soft parts decayed and the hard coral skeleton was replaced by minerals like calcite or silica over millions of years.

Uses & applications

Educational, fossil collecting, decorative items, and scientific research into ancient marine paleoenvironments.

Geological facts

Rugose corals are commonly called horn corals due to their distinct horn-like, curved shape. They were solitary or colonial marine animals that lived on the ocean floor and went extinct during the Permian-Triassic extinction event.

Field identification & locations

Easily identified by their conical, horn-like shape and distinct vertical septa (internal ridges) radiating inside the calyx. Frequently found in limestone quarries, ancient seabed exposures, and gravel beds worldwide.