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 August 23, 2026More fossil →

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Physical properties

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.