sedimentary
Fossiliferous Limestone (Coquina / Shell Limestone)
Bioclastic Limestone (CaCO3)
Hardness: 3-4 (Mohs scale); Color: Cream, tan, or light grey; Luster: Dull to earthy; Texture: Coarse-grained with visible fossil fragments; Composition: Primarily calcite with organic debris.
- Hardness
- 3-4 (Mohs scale)
- Color
- Cream, tan, or light grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: Cream, tan, or light grey; Luster: Dull to earthy; Texture: Coarse-grained with visible fossil fragments; Composition: Primarily calcite with organic debris.
Formation & geological history
Formed in high-energy marine environments (beaches or shallow lagoons) where accumulation of broken shell fragments and skeletal remains are cemented together by calcium carbonate. Most specimens date from the Phanerozoic eon.
Uses & applications
Used in the production of lime and cement, as a decorative veneer in architecture, as gravel for roadbeds, and as educational specimens for fossil hunters.
Geological facts
In Puerto Rico and Florida, a specialized form called Coquina was historically used to build massive forts because its porous structure could absorb the impact of cannonballs without shattering.
Field identification & locations
Identify in the field by looking for visible shell impressions or tubes with a granular, clastic texture. It will react and fizz (effervesce) if a weak acid like vinegar is applied. Commonly found in coastal regions or areas that were ancient seabeds.
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