fossil

Rugose Coral Fossil

Order Rugosa (Tetracorallia)

Hardness: 3-4 (Calcite replacement). Color: Gray, tan, or brown. Luster: Dull/earthy. Structure: Radial septa (petals or spokes) emanating from a central point, often in a horn-like or cylindrical shape.

Hardness: 3-4 (Calcite replacement)
Color: Gray, tan, or brown
Luster: Dull/earthy

Identified July 21, 2026More fossil →

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Physical properties

Formation & geological history

Formed through the petrification of marine organisms during the Paleozoic era (approx. 488 to 251 million years ago) in shallow, warm tropical seas. The original calcium carbonate skeleton is often replaced by silica or calcite during burial.

Uses & applications

Scientific study of evolutionary history, educational specimens, lapidary carvings when silicified, and common collector items.

Geological facts

Also known as 'Horn Corals' due to their frequent conical shape. Unlike modern corals, these corals usually lived as solitary individuals rather than part of massive reefs. They went extinct during the Great Permian Extinction.

Field identification & locations

Identify by looking for characteristic 'septa' or radiating lines in a circular cross-section. Commonly found in limestone beds, gravel pits, and riverbanks in the Midwest USA (Michigan, Ohio, Indiana) and other global Paleozoic sites.