Sedimentary Rocks D. Crowley, 2008

Sedimentary Rocks To know how sedimentary rocks are formed

Sedimentary Rocks Compare the sand and the sedimentary rock sandstone What are the differences between them? Why is the sandstone so much harder? SandSandstone

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

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…

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 minutes

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

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

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