fossil
Fossil Coral (Rugose Coral)
Order Rugosa (Tetracorallia)
Hardness: 3-4 (if calcified) or 7 (if silicified/agatized); Color: Tan, grey, creamy white; Luster: Dull to waxy; Features a radial skeletal structure known as septa appearing as tiny spokes.
- Hardness
- 3-4 (if calcified) or 7 (if silicified/agatized)
- Color
- Tan, grey, creamy white
- Luster
- Dull to waxy
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Physical properties
Hardness: 3-4 (if calcified) or 7 (if silicified/agatized); Color: Tan, grey, creamy white; Luster: Dull to waxy; Features a radial skeletal structure known as septa appearing as tiny spokes.
Formation & geological history
Formed from the calcium carbonate skeletons of solitary or colonial corals that lived in warm, shallow marine environments primarily during the Paleozoic era (approx. 500 to 250 million years ago).
Uses & applications
Scientific study, educational collections, ornamental lapidary work (when agatized), and jewelry such as pendants or beads.
Geological facts
Also known as 'Horn Corals' due to their horn-like shape, Rugose corals went extinct during the Great Permian Extinction. They are distinct because they always have four primary septae.
Field identification & locations
Commonly found in limestone outcrops or as weathered stones in riverbeds and Great Lakes shorelines. Look for the 'sunburst' or radial pattern on the cross-section of the stone.
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