sedimentary
Fossiliferous Limestone (Coquina / Shell Limestone)
CaCO3 (Calcium Carbonate)
Hardness: 3 (Mohs scale), Color: Cream, tan, or light grey, Luster: Dull/earthy to pearly, Structure: Clastic or bio-clastic (visible shell fragments), Specific Gravity: 2.3-2.7
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Physical properties
Hardness: 3 (Mohs scale), Color: Cream, tan, or light grey, Luster: Dull/earthy to pearly, Structure: Clastic or bio-clastic (visible shell fragments), Specific Gravity: 2.3-2.7
Formation & geological history
Formed in shallow marine environments where organic debris like shells and coral accumulate and are cemented together by calcite. This specimen appears to be from the Cenozoic era, potentially Pliocene or Pleistocene.
Uses & applications
Used primarily in construction for building stone and road aggregate; also used in the manufacture of cement and as a soil conditioner in agriculture.
Geological facts
This rock is essentially a 'living record' of ancient sea life. Some varieties, like Coquina, were used to build the oldest stone fortress in the US, the Castillo de San Marcos, because their porous nature absorbed cannonball impacts rather than shattering.
Field identification & locations
Identify in the field by checking for visible shell imprints or fragments and performing an 'acid test' (it will fizz when in contact with dilute hydrochloric acid or vinegar). Found globally in coastal regions or formerly submerged plains.
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