Rock Identifier
Fossilized sea urchin (Echinoid fossil; commonly Cidaroida or related echinoid) — fossil
fossil

Fossilized sea urchin

Echinoid fossil; commonly Cidaroida or related echinoid

AI-generated identification · may be incorrect

Typically calcite (CaCO₃) stereom, often replaced or coated with silica or iron minerals; Mohs hardness about 3, white to tan, dull-to-slightly pearly luster, and distinctive radial/pentamerous symmetry. The image appears to show a rounded test or spine fragment with surface ornamentation.

Identified More fossil →
Explore Fossilized sea urchin in the encyclopedia →

Identify your own rocks.

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

App StoreGoogle Play

Physical properties

Typically calcite (CaCO₃) stereom, often replaced or coated with silica or iron minerals; Mohs hardness about 3, white to tan, dull-to-slightly pearly luster, and distinctive radial/pentamerous symmetry. The image appears to show a rounded test or spine fragment with surface ornamentation.

Formation & geological history

Marine echinoids lived from the Ordovician to the present; complete fossil tests are especially common in Cretaceous and younger limestones. Burial and mineralization preserve the porous calcitic skeleton over geologic time.

Uses & applications

Primarily a collector, educational, and decorative specimen; occasionally used in jewelry or lapidary work when stable and attractive.

Geological facts

Echinoid skeletons have five-part symmetry, even when weathering obscures it. Individual spines can resemble small carved stones, while intact tests show petal-like ambulacra.

Field identification & locations

Look for fivefold symmetry, repeated plate patterns, tiny tubercles, and a porous calcite texture; acid may weakly fizz, though testing can damage it. Common in marine sedimentary rocks worldwide, including England, France, Morocco, and the U.S.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

fossil
Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

fossil