sedimentary

Fossilized Sea Urchin Spines

Echinoidea (Cidaroid spines)

AI-generated identification · may be incorrect

Hardness: 3 (calcite); Color: Pale grey, tan, or greenish; Luster: Dull to earthy; Shape: Cylindrical, tapered, or club-shaped with a basal attachment ring; Cleavage: Rhombohedral (if recrystallized).

Hardness: 3 (calcite)
Color: Pale grey, tan, or greenish
Luster: Dull to earthy

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the permineralization of sea urchin spines in marine environments. These specimens are typically from the Cretaceous or Jurassic periods (approx. 66–200 million years ago) and are often found in limestone or chalk deposits.

Uses & applications

Used primarily as educational specimens, collector's items, and occasionally in eccentric jewelry pieces.

Geological facts

In folklore, particularly in England, these fossils were sometimes called 'thunderbolts' or 'fairy bolts.' Unlike modern urchins whose spines fall off easily after death, these thicker club-like cidaroid spines are more robust and more likely to fossilize.

Field identification & locations

Identify in the field by their distinct symmetrical ridging or 'warts' on the surface and the circular attachment point at the base. Commonly found in limestone quarries or coastal chalk cliffs.