Rocks and Limestone

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6 mark question:
The Cliffs of Dover are made from chalk which is calcium carbonate. How did the CaCO3
come to be in the rocks that make the cliff?
1. Sediments from eroded and weathered rocks settle at the bottom of the sea.
2. More sediments get deposited in layers
3. Some remains of dead sea creatures get trapped between the layers.
4. The shells of the sea creatures are made of CaCO3
5. The pressure of the sediments on top compress the bottom layers
6. Water gets squeezed out
7. Salt crystals cement the sediments together.
What do they look like- how will you identify them?
Have layers
May have fossils- the shells from these react with acid rain.
The chemical in the shells is calcium carbonate :
o calcium carbonate + acid calcium salt + water+ carbon dioxide
Soft ­ the sediments are only held together by salt crystals
Examples: limestone, sandstone, chalk
Igneous Rocks:
6 mark question
Not all igneous rocks are exactly the same. Describe how the two types of igneous
rocks are formed.
1. Hot magma rises through volcanoes when they erupt
2. Some of the hot magma comes out of the volcano as lava
3. The lava cools rapidly and crystallises into rocks
4. These rocks are called extrusive igneous rocks
5. They usually have small interlocking crystals
6. Sometimes the hot volcanic gases trapped inside them make them porous.
7. Some of the hot magma may also be trapped in pockets inside the volcano
8. This cools slowly and crystallise into rocks
9. These rocks are called intrusive igneous rocks
10. They usually have large interlocking crystals.
What do the rocks look like:
Sparkly- because of the crystals
Very hard
Some may be light for their size ­ they are porous
Examples: granite, pumice, basalt, obsidian
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1. Old rocks get buried deep underground
2. They end up close to the Earth's mantle
3. The heat from below and the pressure from above change the rocks
4. Igneous rocks- their crystals smooth out and become harder
5. Sedimentary rocks ­ the gaps between the sediments get squeezed together and are `glued'
together by stronger salt crystals.
Examples: marble, alabaster
Which rocks get eroded?
This means worn away by: wind, rain, running water, freeze-thaw, trees growing
Soft rocks ­ sedimentary.…read more

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Local communities benefit from the jobs the quarry provides
7. Exporting limestone improves the economy of the country
8. Having the quarry close to the factories reduces the use of fossil fuels burnt in transporting
the raw materials
9. At the end of the project the land can be redeveloped for farming
Thermal Decomposition:
Nearly all of limestone's uses involves thermal decomposition of the CaCO3.
Thermal decomposition is breaking down of a compound using heat.
When carbonates decompose they form oxide plus carbon dioxide.
e.…read more

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