sedimentary
Echinoid Fossil (Commonly called a Sea Urchin or Heart Urchin)
Phylum Echinodermata, Class Echinoidea
Hardness: 3 (Calcite-based), Color: Off-white to tan or light brown, Luster: Dull/Earthy, Crystal Structure: Hexagonal (as replaced by calcite), Cleavage: None (fossilized), Specific Gravity: 2.7
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Physical properties
Hardness: 3 (Calcite-based), Color: Off-white to tan or light brown, Luster: Dull/Earthy, Crystal Structure: Hexagonal (as replaced by calcite), Cleavage: None (fossilized), Specific Gravity: 2.7
Formation & geological history
Formed through the process of permineralization where the skeletal test of a sea urchin is filled with minerals like calcite or silica. Generally found in marine sedimentary layers ranging from the Ordovician period to the present (approx. 450 million years old to modern).
Uses & applications
Primary use is for educational purposes, paleontological study, and as decorative items for fossil collectors. Some limestone containing these fossils is used in construction.
Geological facts
Echinoids have been living in the oceans for over 450 million years. In folklore, fossilized echinoids were often called 'thunderstones' or 'fairy loaves' and were believed to have magical properties to prevent bread from going stale.
Field identification & locations
Identify in the field by looking for a five-fold radial symmetry (pentamerism) and a dome or heart-like shape in chalk or limestone deposits. Commonly found in the UK (Dorset/Kent), the USA (Texas/Florida), and Northern Africa.
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