Rock Identifier
Fossil Solitary Rugose Coral (Horn Coral) (Order Rugosa (e.g., Caninia, Zaphrentis, or Streptelasma)) — fossil
fossil

Fossil Solitary Rugose Coral (Horn Coral)

Order Rugosa (e.g., Caninia, Zaphrentis, or Streptelasma)

Hardness: 3 (calcite matrix) to 7 (if silicified/replaced by quartz); Color: Grayish-brown to beige, often weathered; Luster: Dull to earthy; Structure: Radially arranged septa visible in cross-section forming a cup-like or disk-like corallite structure.

Hardness
3 (calcite matrix) to 7 (if silicified/replaced by quartz)
Color
Grayish-brown to beige, often weathered
Luster
Dull to earthy
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Physical properties

Hardness: 3 (calcite matrix) to 7 (if silicified/replaced by quartz); Color: Grayish-brown to beige, often weathered; Luster: Dull to earthy; Structure: Radially arranged septa visible in cross-section forming a cup-like or disk-like corallite structure.

Formation & geological history

Formed during the Paleozoic Era (Ordovician through Permian periods, approximately 488 to 251 million years ago). They were solitary marine organisms that secreted a calcium carbonate skeleton on the seafloor, later permineralized and preserved within marine limestone or shale sedimentary beds.

Uses & applications

Mainly collected by fossil enthusiasts, educational institutions, and display items. High-quality specimens are polished or cut to showcase the radial internal pattern.

Geological facts

Rugose corals are extinct horn corals that died out during the Permian-Triassic mass extinction event around 252 million years ago. Unlike modern scleractinian corals, rugose corals added septa in four distinct spaces as they grew.

Field identification & locations

Identified by the radial lines (septa) emanating from a central axis, resembling a flower, starburst, or horn-like cross-section. Commonly found in limestone deposits, gravel bars, and stream beds throughout North America, Northern Europe, and Asia.

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