sedimentary
Fossiliferous Limestone (Coquina)
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3-4 (Mohs); Color: Grey, tan, or buff; Luster: Dull/Earthy; Structure: Massive with visible bioclasts; Cleavage: None (conchoidal to uneven fracture); Specific Gravity: 2.3-2.7
- Hardness
- 3-4 (Mohs)
- Color
- Grey, tan, or buff
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Grey, tan, or buff; Luster: Dull/Earthy; Structure: Massive with visible bioclasts; Cleavage: None (conchoidal to uneven fracture); Specific Gravity: 2.3-2.7
Formation & geological history
Formed in marine environments from the accumulation of organic debris such as shell fragments, coral, and microfossils. These are compacted and cemented over millions of years by calcite. Geological age ranges from Paleozoic to Cenozoic eras.
Uses & applications
Used primarily in the construction industry as crushed stone for road base, concrete aggregate, and as a primary ingredient in cement production. High-quality slabs are used for architectural cladding and decorative tiles.
Geological facts
This specimen contains 'packstone' or 'wackestone' textures, which provide clues to the energy of the water during deposition. Famous examples include the walls of the Castillo de San Marcos in Florida, made of a specific shell limestone called Coquina.
Field identification & locations
Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. Look for small circular or curved patterns representing cross-sections of shells or marine organisms. Commonly found in areas that were once prehistoric seafloors, like the Midwestern USA or coastal regions.
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