sedimentary
Fossiliferous Limestone (Coquina / Shell Limestone)
Bioclastic Limestone (CaCO3)
Hardness: 3-4 (Mohs scale); Color: Tan, beige, gray, or white; Luster: Dull to earthy; Structure: Clastic/Biogenic, containing visible shell fragments embedded in a fine-grained matrix; Cleavage: None (fractures irregularly); Specific gravity: 2.3–2.7.
- Hardness
- 3-4 (Mohs scale)
- Color
- Tan, beige, gray, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: Tan, beige, gray, or white; Luster: Dull to earthy; Structure: Clastic/Biogenic, containing visible shell fragments embedded in a fine-grained matrix; Cleavage: None (fractures irregularly); Specific gravity: 2.3–2.7.
Formation & geological history
Formed in marine environments through the accumulation of organic debris such as shell fragments, coral, and skeletal remains. These fragments are compacted and cemented over millions of years, often dating from the Paleozoic to the Cenozoic Eras.
Uses & applications
Primarily used in construction as an aggregate for roads, cement production, and as building stone. High-quality specimens are used in landscaping, as educational fossil samples, or for lapidary work (if the stone is dense enough to take a polish).
Geological facts
This rock is proof of ancient sea levels; finding it in land-locked areas indicates that the location was once under a shallow ocean. It often reacts (fizzes) when touched with a weak acid like vinegar due to its calcium carbonate content.
Field identification & locations
Identify in the field by looking for distinct circular or u-shaped shell imprints and a 'gritty' texture. It is commonly found in coastal regions, ancient sea beds, and limestone quarries globally. Collectors should look for well-preserved, detailed fossils protruding from the matrix.
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