sedimentary
Fossilized Rugose Coral
Rugosa (Order Rugosa, typically fossilized in Limestone)
Hardness: 3-4 (Calcite), Color: Grey, white, or tan, Luster: Dull to earthy, Structure: Solitary 'horn' shape or colonial, featuring radial septa (lines) visible in cross-section.
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Physical properties
Hardness: 3-4 (Calcite), Color: Grey, white, or tan, Luster: Dull to earthy, Structure: Solitary 'horn' shape or colonial, featuring radial septa (lines) visible in cross-section.
Formation & geological history
Formed during the Paleozoic era (Ordovician to Permian) in shallow marine environments. The skeleton of the coral was replaced by calcite or silica over millions of years.
Uses & applications
Paleontological study, educational collections, decorative display, and jewelry (when agatized).
Geological facts
Commonly known as 'horn corals' because solitary species resemble a bull's horn. They went extinct during the Permian-Triassic extinction event, the most severe extinction in Earth's history.
Field identification & locations
Identify by looking for the distinct 'wheel-spoke' radial septa in the center of the rounded stone. Often found in limestone outcrops, river beds, or gravel pits in the Midwestern US and UK.
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