sedimentary

Coquina

Biogenic Limestone (Calcite/Aragonite)

Hardness: 2-3 (Mohs scale); Color: tan, cream, or light brown; Luster: dull to earthy; Structure: clastic/fragmental; Composition: loosely cemented shells and coral fragments; Cleavage: none (ruptures along shell boundaries); Specific Gravity: ~2.3-2.5

Hardness: 2-3 (Mohs scale)
Color: tan, cream, or light brown
Luster: dull to earthy

Identified April 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in high-energy marine or lacustrine environments (beaches/reefs) where shells are broken by wave action and later cemented by calcium carbonate (calcite). Typically younger formations from the Pleistocene or Holocene epochs.

Uses & applications

Used historically as a unique building material, in road base construction, as landscaping gravel, and as a source of lime for fertilizer.

Geological facts

Famous for its use in the construction of the Castillo de San Marcos in St. Augustine, Florida; the rock's porous nature allowed it to absorb cannonball impacts rather than shattering.

Field identification & locations

Identifiable by its 'shredded wheat' appearance consisting of visible shell fragments. Found primarily along coastal regions like Florida, North Carolina, and Shark Bay, Australia. Collectors should look for soft, crumbly textures with high fossil content.