Transcript Sedimentary Rocks

Sedimentary Rocks
D. Crowley, 2008
Sedimentary Rocks
To know how sedimentary rocks are formed
Sedimentary Rocks
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Compare the sand and the sedimentary rock sandstone
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What are the differences between them? Why is the sandstone so
much harder?
Sand
Sandstone
Sandstone Formation
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Sedimentary rocks often have layers showing deposition of sediment
through different time periods
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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)
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Sedimentary rocks often contain fossils
Sandstone Formation
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Sandstone was originally loose sand on the floor. Since then the
grains have become stuck together
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You are going to investigate
how this could have
happened…
Sedimentary Experiment
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Smear a small amount of petroleum jelly around the inside of the syringe
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Make some sand damp in a plastic cup by adding a small amount of water to it:
fill you syringe with this damp sand
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Put your fingers over the end of the syringe and press the plunger in as hard as
you can
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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
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Leave your pellets to dry for 10-15 minutes
Sedimentary Experiment
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Whilst the pellets dry, predict which will be the strongest and why
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Then design an experiment to test their strength and carry this out
Sedimentary Formation
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Rocks are deposited at the bottom of a lake / sea (after being transported from rivers)
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The deposited rocks build up in layers, called sediments (this is sedimentation)
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The weight of the sediments on top squashes the sediments at the bottom
(compaction)
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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 Formation
Sedimentary Formation
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Sedimentary rocks has the oldest layers at the bottom and the youngest layers at the
top
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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