fossil

Fossilized echinoid (sea urchin), likely a regular echinoid

Echinodermata; class Echinoidea, calcitic stereom preserved as calcite (CaCO₃)

AI-generated identification · may be incorrect

Cream-to-tan, fine-grained, dull to slightly waxy surface with raised ambulacral/petal-like structures and a rounded test shape; calcite is Mohs 3, has imperfect cleavage, and reacts with dilute hydrochloric acid. The specimen appears weathered or partially mineral-replaced.

Identified August 21, 2026More fossil →

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Physical properties

Formation & geological history

Formed from the calcitic shell (test) of a marine sea urchin, later buried and lithified in carbonate sediment; exact age is uncertain from the image, commonly Mesozoic–Cenozoic in comparable specimens.

Uses & applications

Primarily a teaching and collecting specimen; polished or attractive examples are sold as curios, while fossil-rich limestone may be used decoratively or as aggregate.

Geological facts

Sea urchin tests consist of many interlocking calcite plates and typically show fivefold radial symmetry; spines and detailed pore pairs may be lost through weathering.

Field identification & locations

Identify by fivefold symmetry, repeated plate patterns, and acid reaction, distinguishing it from a concretion. Common in marine limestones and chalks worldwide, including Europe, North Africa, the Middle East, and North America.