sedimentary

Coquina

Bioclastic Limestone (composed primarily of CaCO3)

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale); Color: White, tan, or cream; Luster: Dull/Earthy; Structure: Clastic/Biochemical (poorly cemented shell fragments); Cleavage: None (friable/crumbly); Specific Gravity: 2.3-2.6

Hardness: 2-3 (Mohs scale)
Color: White, tan, or cream
Luster: Dull/Earthy

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine environments (beaches or shallow reefs) where mechanical wave action accumulates shell fragments. Most existing coquina deposits are from the Pleistocene or Holocene epochs.

Uses & applications

Historically used as a building stone (e.g., Castillo de San Marcos); currently used in road base, landscaping, and the manufacture of cement.

Geological facts

Coquina is unique because it is porous and compressible, which allowed it to absorb cannonballs during colonial battles rather than shattering like solid stone. It is essentially a 'rock made of shells.'

Field identification & locations

Identify in the field by its 'granulized' appearance made of visible shell fragments and its vigorous effervescence when exposed to dilute HCl. It is commonly found along the Atlantic coast, particularly in Florida.