sedimentary

Coquina

Bioclastic Limestone (Coquina)

AI-generated identification · may be incorrect

Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline; Cleavage: None (uneven fracture); SG: 1.2 - 2.0 (often porous).

Hardness: 3 (Mohs scale)
Color: Tan, beige, or white
Luster: Dull to earthy

Identified March 8, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: Tan, beige, or white; Luster: Dull to earthy; Crystal structure: Amorphous/microcrystalline; Cleavage: None (uneven fracture); SG: 1.2 - 2.0 (often porous).

Formation & geological history

Formed in high-energy marine environments (beaches/reefs) by the accumulation and lithification of shells, coral fragments, and other biotic debris over thousands to millions of years.

Uses & applications

Used primarily as road base material, decorative landscaping stone, and historically as a building material for forts and churches (due to its high compressibility and resistance to cannon fire).

Geological facts

Famous for its role in the construction of the Castillo de San Marcos in St. Augustine, Florida. It is effectively a 'natural concrete' made entirely of sea life.

Field identification & locations

Identify in the field by its distinct 'oatmeal' or 'shredded wheat' texture consisting of visible shell fragments. Found typically along coastal regions like Florida, North Carolina, and Baja California.