1. Sedimentary Rocks D. Crowley, 2008

2. Sedimentary Rocks To know how sedimentary rocks are formed

3. Sedimentary Rocks • Compare the sand and the sedimentary rock sandstone • What are the differences between them? Why is the sandstone so much harder? Sand Sandstone

4. Sandstone 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

5. Sandstone 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…

6. Sedimentary Experiment • 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

7. Sedimentary Experiment • Whilst the pellets dry, predict which will be the strongest and why • Then design an experiment to test their strength and carry this out

8. Sedimentary Formation • 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

9. Sedimentary Formation

10. Sedimentary Formation

11. Sedimentary Formation • 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