fossil

Echinoid Fossil in Flint or Chert Nodule

Echinoidea embedded in sedimentary silica (SiO2)

Hardness of 7 on the Mohs scale (due to the surrounding flint/chert matrix); colors range from grey to white with dark mottling; dull to waxy luster; cryptocrystalline quartz structure; conchoidal fracture.

Identified July 31, 2026More fossil →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (approximately 66 to 145 million years ago) when marine organisms (sea urchins) became encased in silica-rich ooze on ancient seafloors, which subsequently diagenetically altered into hard flint or chert nodules.

Uses & applications

Valuable collector specimen, educational tool for paleontology, and occasionally used in amateur lapidary work or display.

Geological facts

Many ancient cultures considered fossilized sea urchins (often called shepherd's crowns or fairy loaves) to be thunderstones capable of protecting homes from lightning and evil spirits.

Field identification & locations

Can be identified in the field by its distinct spherical or button-like nodule shape featuring the unmistakable pentameral (five-part) radial symmetry or fossilized plates of an ancient echinoid on the surface. Commonly found in chalk deposits and gravel beds in regions like Western Europe and parts of North America.

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Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Sedimentary Outcrop (Sandstone/Shale)

Sedimentary bedrock formation (variable composition)

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Chert with Fossil Brachiopod

Microcrystalline Quartz (SiO2) with Calcitic Brachiopod inclusion

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

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