sedimentary

Coquina

Bioclastic Limestone (Calcium Carbonate, CaCO3)

Hardness: 2-3 (Mohs scale); Color: Tan, brownish-yellow, or whitish with reddish-brown patches; Luster: Dull to earthy; Structure: Fragmental/clastic; Cleavage: None (friable); Specific Gravity: 2.2-2.4

Hardness: 2-3 (Mohs scale)
Color: Tan, brownish-yellow, or whitish with reddish-brown patches
Luster: Dull to earthy

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (shores or reefs) where shells are broken by wave action and later cemented together by calcium carbonate. Most deposits are from the Pleistocene to Holocene epochs.

Uses & applications

Historically used as a building stone (notable in Florida and Spain) because it is soft to cut but hardens over time. Used today as road base material, decorative landscaping stone, and in the production of lime.

Geological facts

Coquina is famous for its defensive properties in fortifications like the Castillo de San Marcos; instead of shattering under cannon fire, the porous rock 'absorbed' the cannonballs like a sponge.

Field identification & locations

Identify by its 'oatmeal' or 'granola' appearance made entirely of visible shell fragments. Found primarily along coastlines in Florida, North Carolina, and Australia. Collectors should look for intact shells within the matrix.

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