Coquina

A rock made almost entirely of broken shells loosely cemented together.

Coquina specimen — Photo: PaleoNeolitic, CC BY 4.0, via Wikimedia Commons

How to identify coquina

Visible shell pieces throughout.
Porous and light.
Fizzes strongly in acid.

Often confused with

Limestone
Limestone is denser and shells are less obvious.
Compare side by side
Conglomerate
Conglomerate is made of pebbles, not shells.
Compare side by side

Where it's found

St. Augustine, Florida
Shark Bay, Australia
North Carolina

Uses

Building blocks in coastal areas.

Rock tumbling

Not suitable for tumbling.

Did you know?

Cannonballs sank into the coquina walls of Florida's Castillo de San Marcos instead of shattering them.

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