sedimentary
Coquina
Biogenic Limestone (mostly Calcium Carbonate, CaCO3)
Hardness: 2-3 (Mohs scale); Color: White, tan, or grey; Luster: Dull to earthy; Crystal structure: Non-crystalline mass of shell fragments; Cleavage: None; Specific gravity: 2.3-2.4.
- Hardness
- 2-3 (Mohs scale)
- Color
- White, tan, or grey
- Luster
- Dull to earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: White, tan, or grey; Luster: Dull to earthy; Crystal structure: Non-crystalline mass of shell fragments; Cleavage: None; Specific gravity: 2.3-2.4.
Formation & geological history
Formed in high-energy marine environments (beaches or shallow reefs) where wave action accumulates shell fragments. Over time, these are weakly cemented together by calcium carbonate. Most deposits are relatively young geologically (Pleistocene or Holocene).
Uses & applications
Historically used as a building material for forts and homes; currently used in landscaping, as a source of lime for agriculture, and as road base material.
Geological facts
Because it is porous and relatively soft, coquina was famous for its use in Spanish forts like Castillo de San Marcos; instead of shattering under cannon fire, the walls would 'absorb' the cannonballs.
Field identification & locations
Identify in the field by its distinct 'oatmeal' texture made of visible shells and shell fragments. It will effervesce (fizz) when exposed to weak acid like vinegar. Found commonly along the coasts of Florida and the Caribbean.
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