sedimentary

Coquina

Biogenic Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 2-3 (Mohs scale); Color: tan, grey, or off-white; Luster: earthy or dull; Crystal Structure: contains visible shell fragments; Cleavage: none; Specific Gravity: varies (low due to porosity)

Hardness: 2-3 (Mohs scale)
Color: tan, grey, or off-white
Luster: earthy or dull

Identified June 19, 2026More sedimentary →

Explore Coquina in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 2-3 (Mohs scale); Color: tan, grey, or off-white; Luster: earthy or dull; Crystal Structure: contains visible shell fragments; Cleavage: none; Specific Gravity: varies (low due to porosity)

Formation & geological history

Formed in high-energy marine environments where shell fragments and coral debris accumulate and are weakly cemented together by calcium carbonate. Most specimens date back to the Holocene or Pleistocene epochs.

Uses & applications

Historically used as a building material for forts and homes (especially in Florida), as road base material, and occasionally in landscaping or as a source of lime.

Geological facts

Coquina was used to build the Castillo de San Marcos in St. Augustine, Florida. Because it is porous, it absorbed cannonball impacts rather than shattering, making the fort nearly indestructible.

Field identification & locations

Identify it by its coarse, 'oatmeal-like' texture made of visible broken seashells. It reacts (fizzes) strongly when a drop of diluted hydrochloric acid or vinegar is applied. Common along coastal regions.