Shop Windows to the Universe

Our Glaciers: Then and Now activity kit helps you see the changes taking place in glaciers around the world. See all our activity kits and classroom activities.
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.
Click on image for full size
Courtesy of Larry Fellows and the Arizona Geological Survey

Clastic Rocks

Clastic sedimentary rocks are made up of fragments of other rocks called sediment. Larger pieces are called grains or clasts. Small, muddy pieces are called matrix. In a clastic sedimentary rock, the clasts and the matrix are held together with mineral crystals called cement.

There are many different types of clastic sedimentary rocks. They can be identified based on:

  • The size of clasts (Are they mud, sand, or pebbles?)
  • The range of clast sizes (Are they all of similar size?)
  • The shape of the clasts (Are they rounded or angular?)

The types of sedimentary rocks that are formed in an area depend on the environment where they were deposited. For instance, sandstone, a sedimentary rock made of sand grains, may form in a beach environment or desert sand dunes. Shale, a sedimentary rock made of mud and clay, may form in a swamp, the bottom of a lake, or some other muddy environment. Conglomerate, a sedimentary rock make of gravel and sand, may form from the sediment at the bottom of a stream.

Making a clastic sedimentary rock is a four step process.

Last modified August 25, 2003 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Step 2: Erosion and Transport (Sediments on the Move!)

Sneeze into a pile of dust and the particles fly everywhere. Sneeze into a pile of rocks and they stay put. Thatís because they have more mass. You need more force than a sneeze to move those rocks. Wind...more

Step 3: Deposition (Sediments Settling Down!)

When water or wind loses energy and slows down, sediment can no longer be carried in it. The particles of sediment fall through the water or air and form a blanket of sediment on the bottom of a river,...more

Organic Sedimentary Rocks

The sediment in an organic sedimentary rock is made of fossils! The mineral parts of animals, such as bones and shells, are much more likely to be preserved than the soft tissues, which typically decay....more

Whatís That Mineral?

Each type of mineral is made of a unique group of elements that are arranged in a unique pattern. However, to identify minerals you donít need to look at the elements with sophisticated chemical tests....more

Quartz

Quartz is the second most common mineral in Earthís crust. It is a member of the quartz group, which includes less common minerals such as opal, crystobalite, and coesite. Silica (Si) and Oxygen (O) are...more

Mica Minerals

Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which...more

Feldspar

Feldspar is the most common mineral in the Earthís crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF