sedimentary
Sand Dollar Fossil (Echinoidea)
Class Echinoidea (likely order Clypeasteroida), CaCO3 (Calcite)
Hardness: 3 on Mohs scale; Color: Off-white, grey, or earthen tan; Luster: Dull to chalky; Structure: Pentamerous (five-fold) symmetry with a petal-like pattern; Cleavage: None/Fragmentary.
- Hardness
- 3 on Mohs scale
- Color
- Off-white, grey, or earthen tan
- Luster
- Dull to chalky
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Physical properties
Hardness: 3 on Mohs scale; Color: Off-white, grey, or earthen tan; Luster: Dull to chalky; Structure: Pentamerous (five-fold) symmetry with a petal-like pattern; Cleavage: None/Fragmentary.
Formation & geological history
Formed through permineralization of the calcium carbonate exoskeleton (test) of an irregular sea urchin. These organisms lived in shallow marine environments. Geological age can range from the Eocene (56 million years ago) to the Holocene.
Uses & applications
Primarily used for educational purposes, fossil collecting, and occasionally in jewelry or decorative crafts due to their unique star pattern.
Geological facts
In folklore, they were sometimes called 'mermaid coins' or 'Sailor's coins'. Despite their flat appearance, they are biological relatives of sea urchins and starfish. Many specimens found on beaches are modern, but 'heavy', stone-like versions are true fossils found in sedimentary rock layers.
Field identification & locations
Identify by looking for the 'petaloid' pattern (the five-pointed star) and the flat, disc-like shape. In the field, look for them in limestone or sandstone outcrops near coastal regions or ancient seabeds.
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