Coquina with Shell Fragment

Physical Properties

Hardness: 3 (Mohs scale); Color: Cream, tan, or white; Luster: Dull to pearly (on shell surfaces); Structure: Fragmental/Clastic; Cleavage: None (fractures irregularly).

Formation & Geological History

Formed in high-energy marine environments (beaches/shallow reefs) where shell fragments accumulate and are cemented together by calcium carbonate over hundreds to thousands of years.

Uses & Applications

Used primarily in construction, historically for building forts (like Castillo de San Marcos) due to its shock-absorbing properties, and for landscaping or road base.

Geological Facts

Coquina was historically a vital building material in Florida because it is soft enough to quarry but 'elastic' enough to absorb cannonball impacts rather than shattering.

Field Identification & Locations

Identify by its 'mushy' or 'granola-like' appearance of visible shells. Found along coastlines, particularly in Florida and North Carolina. It will fizz if a drop of vinegar is applied.

Identified on: 4/28/2026

Mode: Standard