sedimentary
Coquina
Bioclastic Limestone (composed of CaCO3)
Hardness: 2-3 (Mohs scale); Color: Tan, brown, white, or yellowish; Luster: Dull to earthy; Crystal structure: Trigonal (microscopic); Cleavage: None/clastic; Specific Gravity: 1.5 - 2.5 (porous).
- Hardness
- 2-3 (Mohs scale)
- Color
- Tan, brown, white, or yellowish
- Luster
- Dull to earthy
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Physical properties
Hardness: 2-3 (Mohs scale); Color: Tan, brown, white, or yellowish; Luster: Dull to earthy; Crystal structure: Trigonal (microscopic); Cleavage: None/clastic; Specific Gravity: 1.5 - 2.5 (porous).
Formation & geological history
Formed in high-energy marine environments (beaches) where shell fragments accumulate and are loosely cemented by calcium carbonate. Most specimens are from the Quaternary or Cenozoic eras.
Uses & applications
Historically used as a building stone (notable in Florida's Castillo de San Marcos) and currently used as road base material, decorative landscaping gravel, and for shoreline restoration.
Geological facts
Because it is porous and soft, coquina was historically valued in fortifications because it would absorb the impact of cannonballs rather than shattering like harder stone.
Field identification & locations
Identified in the field by its 'oatmeal-like' appearance and the presence of visible, unsorted shell fragments. It will effervesce (fizz) strongly when exposed to diluted hydrochloric acid.
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