sedimentary
Horn Coral Fossil
Rugosa (Order Rugosa)
Hardness: 3 (if calcite) to 7 (if silicified); Color: Gray, tan, or white; Luster: Dull to earthy; Structure: Solitary 'horn' shape with internal septa radiating from a center; Cleavage: None (fracture)
- Hardness
- 3 (if calcite) to 7 (if silicified)
- Color
- Gray, tan, or white
- Luster
- Dull to earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 3 (if calcite) to 7 (if silicified); Color: Gray, tan, or white; Luster: Dull to earthy; Structure: Solitary 'horn' shape with internal septa radiating from a center; Cleavage: None (fracture)
Formation & geological history
Formed through the fossilization of marine organisms in shallow sea environments. Most specimens date from the Ordovician to the Permian periods (approx. 488 to 251 million years ago).
Uses & applications
Educational purposes, museum displays, and private geological collections. Rarely used in jewelry as 'fossil coral' cabochons.
Geological facts
Horn corals are extinct. Unlike modern corals, they were solitary organisms that lived on the seafloor. They went extinct during the 'Great Dying' at the end of the Permian period.
Field identification & locations
Identify in the field by the distinct cone shape and the radial pattern (septa) visible on the broken cross-section. Commonly found in limestone outcrops and riverbeds in the Midwest US and UK.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary