sedimentary
Fossiliferous Limestone (Coquina-like)
Biogenic Limestone
Hardness: 3-4 (calcite based); Color: Tan, grey, and white shell fragments; Luster: Dull to earthy; Structure: Clastic fossil fragments in a fine-grained matrix; Cleavage: None (conchoidal to irregular fracture)
- Hardness
- 3-4 (calcite based)
- Color
- Tan, grey, and white shell fragments
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (calcite based); Color: Tan, grey, and white shell fragments; Luster: Dull to earthy; Structure: Clastic fossil fragments in a fine-grained matrix; Cleavage: None (conchoidal to irregular fracture)
Formation & geological history
Formed in shallow marine environments where shell debris (mollusks, brachiopods) accumulates and is cemented together by calcium carbonate over millions of years, typically ranging from the Paleozoic to Cenozoic eras.
Uses & applications
Primarily used in the manufacture of cement, as a building stone (limestone), and as interesting decorative pieces for fossil collectors.
Geological facts
This specimen appears to be a water-worn river or beach stone composed of fossilized shell fragments. In Florida, a similar loosely compacted version is called Coquina and was used to build historical forts like Castillo de San Marcos.
Field identification & locations
Identify in the field by looking for visible shell impressions and testing with a drop of vinegar; it will effervesce (fizz). Commonly found in ancient sea beds, river banks, and coastal areas.
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