sedimentary
Fossilized Oyster Shell (Limestone/Coquina)
Crassostrea (Fossilized Bivalve), Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale for Calcite); Color: Off-white, grey, tan; Luster: Dull/Earthy to Pearly; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral
- Hardness
- 3 (Mohs scale for Calcite)
- Color
- Off-white, grey, tan
- Luster
- Dull/Earthy to Pearly
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Physical properties
Hardness: 3 (Mohs scale for Calcite); Color: Off-white, grey, tan; Luster: Dull/Earthy to Pearly; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral
Formation & geological history
Formed through the accumulation of organic debris in shallow marine environments during the Cenozoic or Mesozoic eras. Over millions of years, pressure and mineralization convert shells into fossiliferous limestone.
Uses & applications
Used primarily in construction (aggregate, cement making), soil conditioning, and as a component of decorative landscaping rocks.
Geological facts
Fossilized oysters are key indicators of paleo-environments, showing where ancient coastlines and estuaries once existed. In some regions, entire roadbeds are built from shell-rich limestone called Coquina.
Field identification & locations
Identify by visible concentric growth lines and a heavy, stony feel compared to a fresh shell. Found in coastal regions, limestone quarries, and dry creek beds where prehistoric seas once stood.
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