sedimentary

Coral Rock (Coquina)

Biogenic Limestone (Calcium Carbonate - CaCO3)

Hardness: 3-4 (Mohs scale), Color: Cream, white, or light gray, Luster: Dull/Earthy, Crystal Structure: Trigonal/Orthorhombic (Aragonite/Calcite), Cleavage: None/Fragmental, Specific Gravity: 2.3-2.7. It has a porous, vuggy texture with visible shell fragments.

Identified January 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and cemented lithification of organic debris such as coral skeletons, shells, and marine organisms. Typically from the Pleistocene to Holocene epoch, found in shallow marine environments or ancient reef sites.

Uses & applications

Used in construction as a building stone (historically for forts and walls), in landscaping, road base material, and sometimes as a source for lime in agriculture.

Geological facts

Many historic structures, like the Castillo de San Marcos in Florida, were built with coquina because it could absorb the impact of cannonballs rather than shattering like harder rock. It is essentially a 'natural concrete' made of biological remains.

Field identification & locations

Identify in the field by its porous, brittle texture and the presence of visible fossil remains or tiny hollows. A simple field test is the acid test; it will vigorously effervesce (fizz) when exposed to a drop of dilute hydrochloric acid or strong vinegar due to the calcium carbonate content.

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