fossil

Fossilized echinoid (sea urchin)

Echinoid test; commonly Cretaceous–Eocene irregular echinoid, calcite (CaCO₃)

AI-generated identification · may be incorrect

Pale tan, rounded, finely granular specimen with radiating petal-like grooves and possible tubercle texture; calcitic, typically Mohs 3–4, dull to slightly waxy luster, no obvious cleavage, specific gravity about 2.7. The visible symmetry strongly suggests a fossil rather than an ordinary pebble.

Identified August 22, 2026More fossil →

Explore Fossilized echinoid (sea urchin) 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 from the mineralized shell (test) of a marine sea urchin, later buried and replaced or infilled by calcite-rich sediment. Similar specimens commonly date from the Cretaceous to Paleogene and occur in shallow-marine limestone deposits.

Uses & applications

Primarily collected, displayed, and used educationally; polished examples are sometimes sold as decorative objects or jewelry components. It has little industrial value as an individual specimen.

Geological facts

Echinoid fossils may preserve five-part radial symmetry, ambulacral petals, and tiny pore pairs or tubercles. Weathering can obscure diagnostic surface details and make the fossil resemble a rounded limestone nodule.

Field identification & locations

Look for fivefold symmetry, petal-shaped ambulacra, and repeated pore/tubercle patterns; confirm with a hand lens and a tiny vinegar or dilute-acid test on an inconspicuous spot, which should fizz if calcitic. Common in marine limestones worldwide, including England, France, Morocco, Texas, and Kansas.