Sedimentary Rocks

What is a Sedimentary Rock? Comes from the word “sediment”. Means “something that settles” Loose material gets naturally cemented together and forms a rock.

What is sediment? Plant Remains Boulders Gravel Sand Silt Clay Animal Remains Salts Boulders Gravel Sand Silt Clay

Suspension Rivers move sediment along. Less dense sediment (silt/clay/animal and plant remains) may be suspended in the water. More dense sediment (rocks/boulders) roll along the bottom.

Forming New Sediments Look at the rocks at your table. What can you say about the shape of the rocks? Along a river, those sharp corners are rubbed off. Those new, smaller sediments will be mixed and form new sedimentary rocks.

As the river widens There is the same amount of water. Velocity is slowed. Since the velocity is slowed, it cannot carry many of the sediments and they settle to the bottom.

Some Rocks Made by Plants or Shells Coal Dead plants fell on older, dead plants Sediment covered them. The pressure over millions of years created coal.

Limestone Made from carbonate materials. Such as calcite Shells and skeletons of ocean animals formed these minerals. Over time, their shells are buried on the ocean floor, covered by sediment and cemented together to form limestone.

Dover Cliffs of England Developed millions of years ago when they were under the ocean.

Review What is a sediment? What is “suspension”?

Review What are the two ways, that we have learned, that sedimentary rocks form? What are two rocks that do not form from other rocks?

Dissolved Minerals Reform Rain water washes over minerals and moves them. Some are dissolved in water. Water flows through cracks in rocks and dissolves the rock. This creates caverns.

Sedimentary Rocks Show the Effects of Wind and Water Sedimentary rocks laid down in layers. Older layers are on the bottom. Fossils can get trapped in a layer and covered by the next layer. Rocks can also show conditions long ago.

Ripples

Grand Canyon