sedimentary
Coquina
Bioclastic Limestone (Coquina)
Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline; Cleavage: None (uneven fracture); SG: 1.2 - 2.0 (often porous).
- Hardness
- 3 (Mohs scale)
- Color
- Tan, beige, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline; Cleavage: None (uneven fracture); SG: 1.2 - 2.0 (often porous).
Formation & geological history
Formed in high-energy marine environments (beaches/reefs) by the accumulation and lithification of shells, coral fragments, and other biotic debris over thousands to millions of years.
Uses & applications
Used primarily as road base material, decorative landscaping stone, and historically as a building material for forts and churches (due to its high compressibility and resistance to cannon fire).
Geological facts
Famous for its role in the construction of the Castillo de San Marcos in St. Augustine, Florida. It is effectively a 'natural concrete' made entirely of sea life.
Field identification & locations
Identify in the field by its distinct 'oatmeal' or 'shredded wheat' texture consisting of visible shell fragments. Found typically along coastal regions like Florida, North Carolina, and Baja California.
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