Rock Identifier
Echinoid Fossil (Echinoidea (Cidaroid or irregular echinoid internal mold)) — fossil
fossil

Echinoid Fossil

Echinoidea (Cidaroid or irregular echinoid internal mold)

AI-generated identification · may be incorrect

Hardness 3 (calcite); color ranges from off-white, tan, to gray; dull to earthy luster; microcrystalline calcite structure.

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Physical properties

Hardness 3 (calcite); color ranges from off-white, tan, to gray; dull to earthy luster; microcrystalline calcite structure.

Formation & geological history

Formed during the Mesozoic to Cenozoic eras when the carbonate test of a sea urchin filled with sediment and fossilized.

Uses & applications

Valued by fossil collectors, used in paleontological research and educational displays.

Geological facts

Commonly known as sea urchin fossils or fairy loaves in folklore. The internal mold preserves the shape of the organism after the original shell dissolves or replaces.

Field identification & locations

Found in marine sedimentary rocks, particularly chalk deposits and limestone formations worldwide. Identify by their spherical to heart-like shapes and faint petaloid patterns.

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Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

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Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

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Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

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Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

fossil