sedimentary
Fossilized Solitary Rugose Coral (Horn Coral)
Order: Rugosa (e.g., Grewingkia or Heliophyllum); composed of Calcite (CaCO3) or Silica (SiO2)
Hardness: 3 (if calcite) to 7 (if silicified); Color: Gray, tan, or brown; Luster: Dull to earthy; Shape: Characteristic horn-like or conical shape with radial septa (lines) visible on the internal surface.
- Hardness
- 3 (if calcite) to 7 (if silicified)
- Color
- Gray, tan, or brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (if calcite) to 7 (if silicified); Color: Gray, tan, or brown; Luster: Dull to earthy; Shape: Characteristic horn-like or conical shape with radial septa (lines) visible on the internal surface.
Formation & geological history
Formed in warm, shallow marine environments during the Paleozoic Era (approx. 488 to 251 million years ago). The specimen is a permineralized skeleton of a marine invertebrate.
Uses & applications
Primarily primarily used for educational specimen collecting and geological dating (index fossils). Larger or high-quality specimens are used in polishing or as decorative pieces.
Geological facts
Rugose corals lived as individual ('solitary') polyps, unlike modern reef-building corals. Most species went extinct during the Great Permian Extinction, making them an important marker for ancient sea floors.
Field identification & locations
Identify in the field by looking for the 'horn' shape and fine radial ribbing. Commonly found in limestone outcrops, riverbeds, and gravel pits across North America (especially the Midwest) and Europe.
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