Fossil Coral (Rugose Coral Fragment)

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.

Identified on: 4/19/2026

Mode: Standard