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

Identified April 11, 2026More sedimentary →

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Physical properties

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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Cone-in-cone structure (Secondary Sedimentary Structure)

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Sandstone

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