sedimentary
Coquina Limestone
Coquina (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Off-white, beige, light tan to grayish; Luster: Dull, earthy; Texture: Coarse-grained, porous, composed of visible shell fragments cemented together.
- Hardness
- 3 on Mohs scale
- Color
- Off-white, beige, light tan to grayish
- Luster
- Dull, earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Off-white, beige, light tan to grayish; Luster: Dull, earthy; Texture: Coarse-grained, porous, composed of visible shell fragments cemented together.
Formation & geological history
Formed in shallow marine, high-energy coastal environments where shell debris accumulates and is lightly cemented by calcite over time. Commonly found along Pleistocene and Holocene marine terraces.
Uses & applications
Used historically as a building material (e.g., Castillo de San Marcos in St. Augustine, Florida) because it absorbs cannonball impacts without shattering. Also used for erosion control riprap, road base material, and landscaping boulders.
Geological facts
Because coquina is porous, it can absorb kinetic energy from projectiles, making it a surprisingly effective historical fortress material. Soft when first quarried, it hardens upon exposure to air.
Field identification & locations
Identified by its pale color, light weight relative to size due to porosity, and visible fragmented sea shells cemented together. Extremely common in coastal regions such as Florida, Texas, and Australia.
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