Rocksday

Limestone

A rock made mostly of calcite, often from shells and skeletons of sea creatures. It dissolves to create caves.

Limestone specimen
Photo: Mike Davis, CC0, via Wikimedia Commons

How to identify limestone

  • Fizzes in dilute acid.
  • Gray to cream, often with shell fossils.
  • A knife scratches it.
  • Weathers into smooth, pitted surfaces.

Often confused with

Where it's found

  • Bedford, Indiana
  • Tura, Egypt
  • Mammoth Cave, Kentucky
  • Yorkshire Dales, England

Uses

Cement, building stone and steelmaking flux.

Rock tumbling

Can be tumbled with care. Fossil-rich pieces polish nicely.

Did you know?

The Empire State Building is clad in limestone from Indiana.

Think you could spot it from a blurry close-up?

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