sedimentary
Fossilized Echinoid (Sea Urchin)
Echinoidea (Class) - Often found as Micraster or Clypeaster specimens
Hardness: 3-4 (Calcite replacement); Color: Tan, grey, or light brown; Luster: Dull/Earthy; Crystal Structure: Amorphous fossil structure; Cleavage: None/Irregular; Specific Gravity: Approx 2.7
- Hardness
- 3-4 (Calcite replacement)
- Color
- Tan, grey, or light brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Calcite replacement); Color: Tan, grey, or light brown; Luster: Dull/Earthy; Crystal Structure: Amorphous fossil structure; Cleavage: None/Irregular; Specific Gravity: Approx 2.7
Formation & geological history
Formed over millions of years through permineralization where silica or calcite replaces the organic structure of a deceased sea urchin buried in marine sediment. These often date back to the Cretaceous or Jurassic periods.
Uses & applications
Used primarily for geological study, educational purposes, or as a decorative item for fossil collectors. In some cultures, they were historically used as amulets called 'thunderstones'.
Geological facts
These fossils often exhibit a five-fold symmetry (pentamerism) visible as five radiating lines from the center, which corresponds to the animal's ambulacral grooves. They are ancestors to modern sand dollars and sea urchins.
Field identification & locations
Identify in the field by looking for dome-shaped rocks with a distinct star-shaped pattern on top. Common in limestone deposits and coastal chalk cliffs. Collectors should check for high-definition preservation of the pore pairs.
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