sedimentary
Fossilized Rugose Coral
Order Rugosa (Calcium Carbonate - CaCO3)
Hardness: 3-4 (calcite base); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Hexagonal/Trigonal (calcite replacement); Features: Radial septa (lines) visible in cross-section.
- Hardness
- 3-4 (calcite base)
- Color
- Tan, beige, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (calcite base); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Hexagonal/Trigonal (calcite replacement); Features: Radial septa (lines) visible in cross-section.
Formation & geological history
Formed in shallow marine environments from the Ordovician to the Permian periods. These are the skeletal remains of solitary or colonial corals that were buried in sediment and lithified over millions of years.
Uses & applications
Used primarily as educational specimens, decorative garden stones, and items for fossil collectors.
Geological facts
Rugose corals are often called 'Horn Corals' because of their horn-like shape. They went extinct during the Great Permian Extinction approximately 251 million years ago.
Field identification & locations
Identified in the field by the distinct radial patterns or 'spokes' within a circular or horn-shaped structure. Commonly found in limestone outcrops and riverbeds in the Midwest US and UK.
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