Junior Certificate Geography Introduction to Rocks

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Junior Certificate Geography Introduction to
Rocks
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• The crust of the earth is made of solid rock.
• There are three types of rocks.
• There are

Igneous Rocks
Sedimentary rocks
Metamorphic rocks.
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• Igneous Rocks
• Igneous means fire formed.
• Igneous rocks form when hot molten magma cools.
• When magma cools ON the earths surface, basalt
  rock is made.
• Volcanic eruptions cause magma to come to the
  earths surface where it cools and hardens.
• This happened in the Giants Causeway where the
  basalt formed into columns.

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Igneous Rocks

• When magma cools IN the earths crust, granite is
  formed.
• Magma can rise into the crust but does not come
  onto the surface of the earth.
• Sometimes this magma lies in a magma chamber
  which feeds volcanic eruptions.
• If the magma in the chamber cools and hardens, it
  turns into granite.
• Granite can be found in the Wicklow Mountains.

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 Sedimentary Rocks

• Sedimentary Rocks are made from sediments.
• Sediments are tiny pieces of rock ( e.g. sand )
  which were worn off other rocks by the weather.
• When these sediments are weathered, they may be
  carried by rivers to the sea where they settle on
  the ocean bed.
• Over time, these sediments build up in layers.
• As this happens, the lowest layers are compressed
  or squashed to form rock.
• Sandstone is an example of a sedimentary rock
  made when layers of sand were compressed on the
  ocean floor.
• Sandstone can be found in County Cork

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Sedimentary Rocks

• Limestone is another example of a sedimentary
  rock but is different to sandstone.
• Limestone is made up of the shells of dead sea
  creatures.
• When these creatures died, they fell to the ocean
  floor where they were covered by more shells and
  other sediments.
• Over time the shells were compressed and hardened
  into limestone rock..
• Limstone covers much of the Central Plain of
  Ireland

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• Metamorphic Rock
• Metamorphic means changed.
• Metamorphic rocks are other rocks which have been
  changed.
• Rocks can be changed by the influence of heat,
  pressure or heat and pressure working together.
• If, when magma rises into the earths crust it
  comes into contact with another rock it, will
  cook the rock and change it into another rock.
  
• For example, Quartzite is a metamorphic rock
  which formed when sandstone was exposed to the
  heat of magma..
• Quarzite can be found on the Great Sugarloaf
  Mountain in County Wicklow.
• Similarly, great heat changes limestone to
  marble.
• Marble can be found in Connemara and Kilkenny

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Metamorphic Rock

• Folding occurs when rock is squeezed due to the
  movement of the plates of the crust.
• When folding happens, rock is put under great
  pressure.
• When Shale (made from mud and silt) is put
  under pressure, it changes into Slate the same
  stuff we put on our roofs.

Finish