Rocksday

Conglomerate

Rounded pebbles and cobbles glued together by finer sand and cement — a fossil riverbed or beach.

Conglomerate specimen
Photo: James St. John, CC BY 2.0, via Wikimedia Commons

How to identify conglomerate

  • Contains rounded pebbles larger than 2 mm.
  • Pebbles of different rock types.
  • Sand or mud fills the gaps.
  • Looks like natural concrete.

Often confused with

Where it's found

  • Montserrat, Spain
  • Kata Tjuta, Australia
  • Roxbury, Massachusetts

Uses

Decorative stone and millstones.

Rock tumbling

Can be tumbled with care. Pebbles can pop out if the matrix is weak.

Did you know?

Roxbury puddingstone is the official state rock of Massachusetts.

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