sedimentary
Fossil Sand Dollar (Echinoidea)
Phylum Echinodermata, Class Echinoidea (likely Dendraster or Scutella)
Hardness: 3-4 (calcite); Color: Grey, tan, or greenish-brown; Luster: Dull to earthy; Crystal structure: Trigonal (per-mineralized calcite); Cleavage: Indistinct; Specific Gravity: 2.7
- Hardness
- 3-4 (calcite)
- Color
- Grey, tan, or greenish-brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (calcite); Color: Grey, tan, or greenish-brown; Luster: Dull to earthy; Crystal structure: Trigonal (per-mineralized calcite); Cleavage: Indistinct; Specific Gravity: 2.7
Formation & geological history
Formed through the fossilization of marine invertebrates that lived on or just below the sandy seabed. After death, their calcareous tests are buried in sediment and mineralized over millions of years (commonly Miocene to Pleistocene epochs).
Uses & applications
Primarily used for educational study, fossil collecting, and occasionally used in jewelry once polished or stabilized.
Geological facts
Sand dollars are a type of 'irregular' sea urchin. Their five-fold symmetry (pentamerism) is visible in the petal-like pattern on the top of the specimen, which served as gas exchange organs for the living animal.
Field identification & locations
Identify by looking for the characteristic 'petal' pattern and flattened discoidal shape. Commonly found on beaches adjacent to fossil-bearing cliffs or in sedimentary rock layers near ancient coastlines. Collectors should look for symmetry and well-preserved surface details.
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