sedimentary
Rugose Coral (Horn Coral) Fossil in Limestone
Order Rugosa (commonly Grewingkia or Zaphrentis genus)
Hardness: 3-4 (calcite matrix); Color: Tan, gray, or brownish-white; Luster: Dull or earthy; Structure: Cone-shaped skeleton with visible septa (radiating lines); Specific gravity: ~2.7
- Hardness
- 3-4 (calcite matrix)
- Color
- Tan, gray, or brownish-white
- Luster
- Dull or earthy
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Physical properties
Hardness: 3-4 (calcite matrix); Color: Tan, gray, or brownish-white; Luster: Dull or earthy; Structure: Cone-shaped skeleton with visible septa (radiating lines); Specific gravity: ~2.7
Formation & geological history
Formed through the fossilization of marine organisms in shallow tropical seas. These lived from the Ordovician to the Permian periods (approx. 488 to 251 million years ago). The specimen is a calcified cast and mold preserved in a limestone or marl matrix.
Uses & applications
Primarily used for educational purposes, stratigraphic dating, and as a popular find for amateur fossil collectors and geologists.
Geological facts
Rugose corals are called 'horn corals' due to their distinctive curved, horn-like shape. Unlike modern corals, many rugose corals lived as solitary individuals rather than in huge reefs.
Field identification & locations
Identified by the radial symmetry of the 'septa' (the lines visible in the end of the cone) and the overall tapered shape. Commonly found in roadcuts and creek beds in the Midwestern United States (like Ohio, Indiana, and Kentucky) and other Paleozoic rock outcrops.
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