Cathedral Rock in Arizona is made of a clastic rock called sandstone. These rocks are more than 250 million years old and are now being weathered and eroded away by the creek.
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Courtesy of Larry Fellows and the Arizona Geological Survey

Clastic Rocks

Many sedimentary rocks are made up of little pieces of other rocks called sediment. Mineral crystals called cement hold the sediment together.

There are many different types of sedimentary rocks. Look closely at your rock and answer these three questions to figure out which type of rock you have! You will probably need to use a magnifying glass to see the little sediment grains.

  • How big are the sediments?
  • Are all of the sediments about the same size?
  • Are the sediments rounded or angular in shape?

Different types of sedimentary rocks form from different environments over thousands of years.

  • Sandstone is made of sand. It can form from a beach or desert sand dunes.
  • Shale is made of mud and clay. It can form in a swamp, the bottom of a lake or some other muddy environment.
  • Conglomerate is made of gravel and sand. It may form from sediments at the bottom of a stream.

There are four steps to make this type of sedimentary rock.

Last modified August 25, 2003 by Lisa Gardiner.

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