fossil

Fossilized Coral

Rugosa / Tabulata coral fossils replaced by silica (Chalcedony/Quartz)

Hardness: 6.5 to 7 on the Mohs scale (due to silicification). Color: Varies widely including tan, brown, gray, and white. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.66.

Hardness: 6
Color: Varies widely including tan, brown, gray, and white
Luster: Vitreous to dull

Identified August 3, 2026More fossil →

Explore Fossilized Coral in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the process of permineralization or replacement, where ancient coral skeletons (dating from the Paleozoic era, hundreds of millions of years ago) were gradually replaced by mineral-rich groundwater carrying silica, preserving the intricate internal structure.

Uses & applications

Used primarily in lapidary work, cabochons for jewelry, decorative display pieces, and by fossil and mineral collectors.

Geological facts

Fossil coral is often the state stone of states with ancient marine history, such as Michigan (Petoskey stone). The distinctive cellular patterns reveal the growth structures of ancient marine invertebrates that lived in shallow tropical seas.

Field identification & locations

Can be identified in the field by characteristic honeycomb or star-like patterns on the weathered surface. Commonly found in sedimentary limestone formations and glacial drift deposits in regions previously covered by ancient oceans.

Other fossil specimens

See all

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil

Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

sedimentary

Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

sedimentary

Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

fossil

Fossiliferous Limestone

Limestone with embedded fossil cross-section

sedimentary

Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

sedimentary