sedimentary
Coquina
Biogenic Limestone (Coquina)
Hardness: 2-3 (Mohs scale); Color: Cream, tan, or grayish-white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline calcite; Cleavage: None (fragmental); Specific Gravity: 1.2-2.3 (often porous).
- Hardness
- 2-3 (Mohs scale)
- Color
- Cream, tan, or grayish-white
- Luster
- Dull to earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: Cream, tan, or grayish-white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline calcite; Cleavage: None (fragmental); Specific Gravity: 1.2-2.3 (often porous).
Formation & geological history
Formed in high-energy marine environments (beaches) where waves deposit shell fragments. Over time, these fragments chemical precipitate calcite to cement together. Most date from the Holocene or Pleistocene epochs.
Uses & applications
Used historically as a building stone (noted for shock absorption), road base material, garden landscaping, and as a source of calcium in agriculture.
Geological facts
Because coquina is porous, it can absorb the impact of cannonballs rather than shattering, which led to its famous use in constructing the Castillo de San Marcos in Florida, USA.
Field identification & locations
Identify by looking for visible, poorly sorted shell or coral fragments cemented together with many voids. Most commonly found along the Atlantic coast of Florida and and in parts of North Carolina.
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