Granite

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Granite

Granite is made up of three minerals: quartz, feldspar and mica.

It is a hard, crystalline rock, which is very resistant to erosion.

It is an intrusive igneous rock.

The main processes that affect it are freeze-thaw and hydrolysis.

A good example area to use in Great Britain is Dartmoor.

Dartmoor

The main granite landforms are tors, which can be found on moors such as Dartmoor and Bodmin Moor. Tors are blocks of granite that have weathered slower than the granite around them, because they have less joints and faults.

The Formation of Tors on Dartmoor:

  • The granite seen on Dartmoor originated as a granite batholith, under the surface of the earth. A batholith is an area of molten rock that has cooled very slowly within the crust, creating a rock with large crystals.
  • Over time the material above the batholith was weathered and removed by rivers and glaciers. As this material was removed there was a reduction of pressure on the granite as there was less above it. This caused it to crack creating joints and bedding planes.
  • Where the joints were close together the most rapid weathering occurred, and quickly broke down the rock. However there were also areas where there were very few joints and so slower weathering occurred. The main form of weathering is freeze-thaw.
  • As this process continued over millions of years, the overlying material was totally removed, leaving behind the tors and valleys seen on Dartmoor.
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Other landforms associated with granite are:

Deep, steep v-shaped valleys, created as the water has exploited and eroded through the cracks in the rock.

Marshes and bogs form due to the underlying impermeable granite preventing water from seeping away, and the high rainfall that many of these areas encounter.

Exfoliated domes can occur in warmer climates, producing spectacular scenery, as seen in Yosemite National Park

Yosemite National Park

Granite areas themselves have limited economic uses.

The soil is usually poor and thin, so little farming takes place, probably just some sheep and cattle grazing.

Because granite is impermeable, and the soil is poor, areas such as Dartmoor are ideal sites for reservoirs.

Historically granite areas were mined, especially in the South-West,for things such as copper, tin and arsenic. Nowadays quarrying occurs, taking a way china clay for pottery and of course granite itself, which is used in building (an excellent example being the city of Aberdeen, which is known as "the Granite City"). Granite is also used for things such as hearths,fireplaces, and gravestones.

Tourism is increasingly becoming important in granite areas. Many tourists just come to take in the fresh air and beautiful scenery, but the towns and villages of these areas are trying to cash in by opening guesthouses, cafes and other tourist facilities.

The Northern half of Dartmoor is also used as an army firing range, with a large camp based just outside of Okehampton. The military uses of the moor have caused conflicts with local farmers, residents and tourists.

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