Sedimentary Rocks

D. Crowley, 2008

Sedimentary RocksSedimentary RocksTo know how sedimentary rocks are formed

Sedimentary RocksSedimentary Rocks Compare the sand and the sedimentary rock sandstone

What are the differences between them? Why is the sandstone so much harder?

Sand Sandstone

Sandstone FormationSandstone Formation Sedimentary rocks often have layers showing deposition

of sediment through different time periods

Sedimentary rocks consist of lots of small grains – these grains are often weakly held together, so the rocks are soft and crumbly (as well as often being porous)

Sedimentary rocks often contain fossils

Sandstone FormationSandstone Formation Sandstone was originally loose sand on the floor. Since

then the grains have become stuck together

You are going to investigate how this could have happened…

Sedimentary Sedimentary ExperimentExperiment

Smear a small amount of petroleum jelly around the inside of the syringe

Make some sand damp in a plastic cup by adding a small amount of water to it: fill you syringe with this damp sand

Put your fingers over the end of the syringe and press the plunger in as hard as you can

Take your thumb away and gently push the sand pellet out of the syringe onto a piece of paper

Repeat this using damp sand and gravel; then repeat again using damp sand and plaster of Paris

Leave your pellets to dry for 10-15 minutes

Sedimentary Sedimentary ExperimentExperiment

Whilst the pellets dry, predict which will be the strongest and why

Then design an experiment to test their strength and carry this out

Sedimentary Sedimentary FormationFormation

Rocks are deposited at the bottom of a lake / sea (after being transported from rivers)

The deposited rocks build up in layers, called sediments (this is sedimentation)

The weight of the sediments on top squashes the sediments at the bottom (compaction)

The water is squeezed out from between the pieces of rock and crystals of different salts form – the crystals form a sort of glue that sticks or cements the pieces of rock together (cementation) which may take millions of years

Sedimentation Compaction Cementation

Sedimentary Sedimentary FormationFormation

Sedimentary Sedimentary FormationFormation

Sedimentary Sedimentary FormationFormation

Sedimentary rocks has the oldest layers at the bottom and the youngest layers at the top

Sedimentary rocks may contain fossils of animals and plants trapped in the sediments as the rock was formed – fossils are only found in sedimentary rocks