Coquina

Physical Properties

Hardness: 2-3 (Mohs scale), Color: tan, buff, or cream, Luster: earthy/dull, Crystal structure: amorphous to microcrystalline, Cleavage: none (highly porous/vesicular), Specific gravity: 1.5-2.0 (low due to porosity)

Formation & Geological History

Formed in high-energy marine environments (beaches) where waves accumulate shell fragments and coral debris. These fragments are loosely cemented together by calcite over thousands of years during the Holocene and Pleistocene epochs.

Uses & Applications

Historically used as a building stone (notable in Florida's Castillo de San Marcos) due to its ability to absorb cannonball impacts. Also used as road base material and in landscaping.

Geological Facts

The word 'coquina' is Spanish for 'small shell' or 'cockle'. Because it is so porous, it doesn't shatter when hit; instead, it compresses, making it an excellent defensive building material.

Field Identification & Locations

Identify by its 'shredded wheat' appearance and visible shell fragments. It will react and fizz when exposed to a drop of cold hydrochloric acid. Common along the Atlantic coast of Florida and North Carolina.

Identified on: 4/30/2026

Mode: Standard