sedimentary

Fossiliferous Limestone with Rugose Coral

Calcium Carbonate (CaCO3) featuring Rugosa (extinct order of solitary and colony corals)

Hardness: 3 (Mohs scale); Color: Earthy brown to gray matrix with cream-colored fossil inclusions; Luster: Dull/Earthy; Structure: Clastic to crystalline matrix containing organic fossil structures; Specific gravity: 2.5-2.7

Hardness: 3 (Mohs scale)
Luster: Dull/Earthy

Identified April 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in warm, shallow marine environments during the Paleozoic era (approx. 488 to 251 million years ago). The coral structures represent ancient reef systems where remains were compressed into stone via lithification.

Uses & applications

Primarily used as geological teaching specimens. When found in large deposits, limestone is used for cement, road base, and architectural building stone.

Geological facts

Rugose corals are also known as 'horn corals' due to their distinctive shape. They went extinct during the Great Permian Extinction, making them an index fossil for early geological time periods.

Field identification & locations

Identify by testing for effervescence with a drop of vinegar (limestone reacts). Look for the radiating 'septa' lines visible in the bleached white sections of this specimen. Common in the Midwest USA and UK.

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