fossil

Fossilized Echinoid / Sea Urchin Internal Mold

Echinoidea internal cast (steinkern)

Hardness varies depending on the mineral replacement (typically Mohs 3 for calcite or 7 for quartz/silica); color ranges from light grey to brown; dull to earthy luster; amorphous crystal structure of the replacement matrix.

Identified August 1, 2026More fossil →

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Physical properties

Formation & geological history

Formed in marine sedimentary environments during the Paleozoic, Mesozoic, or Cenozoic eras. When a sea urchin died, its test (shell) filled with sediment, which then hardened into rock before the original organic shell dissolved away, leaving behind a natural cast.

Uses & applications

Valued by fossil collectors, used in educational displays, and studied in paleontology to understand ancient marine ecosystems.

Geological facts

These distinctive fossils are often referred to colloquially as 'fairy loaves' or 'sugar loaves' in folklore. The characteristic paired indentation pattern corresponds to the ambulacral grooves of the sea urchin.

Field identification & locations

Found in marine sedimentary rock layers worldwide, particularly in limestone, chalk, and sandstone formations. Easily identified by their symmetrical, rounded shape with distinctive star-like or paired pit patterns.

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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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