sedimentary
Coquina or Fossiliferous Limestone
Fossiliferous Calcarenite (CaCO3)
Hardness: 3 (Mohs scale); Color: Cream, tan, or grayish-white; Luster: Dull/Earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite particles; Specific Gravity: 2.7
- Hardness
- 3 (Mohs scale)
- Color
- Cream, tan, or grayish-white
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Cream, tan, or grayish-white; Luster: Dull/Earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite particles; Specific Gravity: 2.7
Formation & geological history
Formed in high-energy marine environments where shell debris and coral fragments accumulate and are cemented by calcium carbonate. Most modern specimens are from the Holocene or Pleistocene epochs.
Uses & applications
Used as a historical building material (especially in Florida), road base material, and as an ornamental stone in landscaping or reef restoration.
Geological facts
Famous for its use in the construction of the Castillo de San Marcos in St. Augustine, Florida. It is unique because it is compressible, allowing it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identify in the field by looking for visible shell fragments, a grainy/pockmarked texture, and a vigorous reaction (fizzing) when tested with diluted hydrochloric acid. Commonly found along coastal areas.
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