sedimentary
Fossiliferous Limestone (Coquina)
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale); Color: Tan, buff, or earth tones; Luster: Dull/Earthy matrix; Structure: Clastic fossil fragments in a fine-grained crystalline matrix; Specific Gravity: 2.3-2.7.
- Hardness
- 3 (Mohs scale)
- Color
- Tan, buff, or earth tones
- Luster
- Dull/Earthy matrix
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Physical properties
Hardness: 3 (Mohs scale); Color: Tan, buff, or earth tones; Luster: Dull/Earthy matrix; Structure: Clastic fossil fragments in a fine-grained crystalline matrix; Specific Gravity: 2.3-2.7.
Formation & geological history
Formed in shallow marine environments where organic debris (shells, coral, and mollusks) accumulates. Over millions of years, pressure and chemical precipitation of calcite cement the fragments together. Most common in Paleozoic to Cenozoic strata.
Uses & applications
Used primarily in construction (road base, concrete aggregate) and agriculture to neutralize soil acidity. High-quality specimens are popular for educational purposes and fossil hobbyist collections.
Geological facts
This specimen contains prominent brachiopod or bivalve molds. In the 1600s, 'Coquina' limestone was used to build the Castillo de San Marcos in Florida because its porous nature allowed it to absorb cannonball impacts rather than shattering.
Field identification & locations
Identify in the field by looking for visible shell impressions or whole shells embedded in a soft, light-colored rock. The rock will effervesce (fizz) when exposed to dilute hydrochloric acid. Commonly found in coastal regions or areas that were ancient seabed.
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