sedimentary
Fossilized Echinoid (Sea Urchin)
Echinoidea (Class), often found as calcitic fossils
Hardness: 3 (calcite composition); Color: Cream to white/light grey; Luster: Dull to earthy; Five-fold radial symmetry (pentamerism); Cleavage: Rhombohedral (on individual plate crystals); Specific Gravity: ~2.7.
- Hardness
- 3 (calcite composition)
- Color
- Cream to white/light grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (calcite composition); Color: Cream to white/light grey; Luster: Dull to earthy; Five-fold radial symmetry (pentamerism); Cleavage: Rhombohedral (on individual plate crystals); Specific Gravity: ~2.7.
Formation & geological history
Formed through the permineralization or recrystallization of marine organisms' calcium carbonate shells within sedimentary layers, typically dating from the Ordovician period to the present.
Uses & applications
Primarily used for geological research, educational purposes, and as a popular collector's item; historically used in some cultures as amulets or 'thunderstones'.
Geological facts
In English folklore, these fossils were often called 'fairy loaves' because they resembled small loaves of bread. They are excellent index fossils used to date the rock layers in which they are found.
Field identification & locations
Identify by looking for a dome or heart shape with five visible lines radiating from the center (ambulacra). Commonly found in chalk pits, limestone quarries, or coastal cliffs.
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