fossil

Coquina and Oyster Fossil Rock

Coquina limestone (Calcium Carbonate, CaCO3) containing fossilized Crassostrea / bivalve shells

Hardness varies from 3 on the Mohs scale for the calcite shells to variable matrix; color is typically tan, buff, or light brown; dull to earthy luster; clastic crystal structure; specific gravity around 2.2-2.7.

Identified July 28, 2026More fossil →

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Physical properties

Formation & geological history

Formed in shallow marine or beach environments where wave action accumulates and cements fragments of shells and coral. Geological age typically ranges from Cenozoic to Mesozoic eras, often associated with coastal sedimentary deposits.

Uses & applications

Used locally as a building stone (historically famous in St. Augustine, Florida for the Castillo de San Marcos), road aggregate, and as a popular specimen for fossil and rock collectors.

Geological facts

Coquina is Spanish for 'shell'. Some coquina formations are soft enough to be quarried with blocks easily cut by hand with a saw, but they harden upon exposure to air as surface moisture evaporates and cements the calcite further.

Field identification & locations

Easily identified by its distinct, highly porous texture made almost entirely of visible, cemented shell fragments and larger embedded fossil bivalves. Found globally in coastal sedimentary strata and ancient marine deposits.

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Chert with Fossil Brachiopod

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Fossilized Crinoid Stem in Limestone

Crinoidea (Class) in Calcium Carbonate (CaCO3) matrix

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Fossiliferous Limestone

Limestone with embedded fossil cross-section

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Fossiliferous Limestone with Crinoid stems

Limestone (CaCO3) containing Crinoidea fossils

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