Rock Identifier
Fossil sea urchin (echinoid) (Fossilized echinoid test, likely a regular sea urchin (Class Echinoidea); exact genus and age require locality and examination) — fossil
fossil

Fossil sea urchin (echinoid)

Fossilized echinoid test, likely a regular sea urchin (Class Echinoidea); exact genus and age require locality and examination

AI-generated identification · may be incorrect

Pale gray-beige, rounded pentaradial form with five ambulacral areas and a central apical feature; dull to slightly earthy luster, fine-grained calcite, and no visible crystal cleavage. Calcite hardness is about Mohs 3, with specific gravity near 2.7;…

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Physical properties

Pale gray-beige, rounded pentaradial form with five ambulacral areas and a central apical feature; dull to slightly earthy luster, fine-grained calcite, and no visible crystal cleavage. Calcite hardness is about Mohs 3, with specific gravity near 2.7; the specimen appears weathered and possibly naturally or artificially polished.

Formation & geological history

The original organism had a porous calcium-carbonate skeleton (test) that was buried in marine sediment and mineralized, commonly during the Mesozoic or Cenozoic. Its precise geological age cannot be determined from the photograph alone.

Uses & applications

Primarily a fossil-collecting and educational specimen; cut or polished echinoids are sometimes sold as decorative curiosities, but this is not a gemstone or construction material.

Geological facts

The five-part symmetry reflects the echinoid body plan, and the radial grooves correspond to ambulacra containing tube feet in life.

Field identification & locations

Identify it by fivefold symmetry, repeated pore-pair rows, and a central apical system; compare with known fossils from the collection locality. Value is typically $5-$30 for a common small specimen, or $30-$100+ if exceptionally complete, prepared, or from a desirable locality.

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