fossil

Fossil coral (likely solitary rugose coral)

Rugosa; possibly genus Heliophyllum or similar

AI-generated identification · may be incorrect

Calcitic fossil with radiating septa and a corallite-like cup; white to tan, dull to slightly waxy luster, Mohs hardness about 3. Specific gravity is roughly 2.6–2.7; original skeletal crystal structure was calcite, commonly recrystallized during fossilization.

Identified August 8, 2026More fossil →

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Physical properties

Formation & geological history

A colonial or solitary marine coral preserved in limestone, likely Paleozoic in age (about 485–252 million years old). Burial, compaction, and mineral replacement preserved the corallite’s radial internal structures.

Uses & applications

Used mainly for education, collecting, lapidary carvings, and decorative polished specimens; not generally valuable as gemstone material.

Geological facts

The radial partitions are called septa and helped support the coral’s soft living tissue. Rugose corals are extinct and are often informally called “horn corals,” though this specimen appears notably rounded or weathered.

Field identification & locations

Identify it by the radiating septa, concentric growth features, and limestone-like matrix or texture; acid testing may fizz if exposed calcite is present. Common examples occur in Paleozoic limestone deposits worldwide, including the United States, Canada, Europe, and Australia.