sedimentary
Fossil Coral (Rugose Coral Fragment)
Rugosa (extinct order of solitary and colonial corals)
Hardness: 3-4 (calcite) or 7 (if silicified/replaced by quartz); Color: Brownish-grey to tan; Luster: Dull to earthy; Structure: Distinguishable radial septa (lines) visible on the cross-section; Cleavage: None.
- Hardness
- 3-4 (calcite) or 7 (if silicified/replaced by quartz)
- Color
- Brownish-grey to tan
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (calcite) or 7 (if silicified/replaced by quartz); Color: Brownish-grey to tan; Luster: Dull to earthy; Structure: Distinguishable radial septa (lines) visible on the cross-section; Cleavage: None.
Formation & geological history
Formed through the fossilization of marine organisms in shallow tropical seas during the Paleozoic era (approx. 488 to 251 million years ago). The organic material was replaced by calcite or silica over millions of years.
Uses & applications
Primarily used as educational specimens, for fossil collecting, and occasionally in lapidary work (jewelry) if highly agatized.
Geological facts
Rugose corals are often called 'horn corals' due to the horn-like shape of the solitary species. They went extinct during the Great Permian Extinction 251 million years ago.
Field identification & locations
Identify in the field by looking for radial symmetry and vertical ridges (septa) in sedimentary rock layers, particularly limestone or shale near ancient reef systems.
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