The Rock Cycle
The concept of the rock cycle is attributed to James Hutton
(1726–1797), the 18th-century founder of modern geology.
The main idea is that rocks are continually changing from one
type to another and back again, as forces inside the earth bring them closer to the surface (where they are weathered, eroded,
and compacted) and forces on the earth sink them back down (where they are heated, pressed, and melted).
So the elements that make up rocks are never created or
destroyed — instead, they are constantly being recycled.
The rock cycle helps us to see that the earth is like a giant
rock recycling machine!
Igneous Rocks
Formation of Basalt - Volcanic Rock
Sedimentary Rocks
Metamorphic rocks
- Igneous rocks are formed when molten rock cools and hardens.
- Igneous rocks have crystals. The large crystals are formend in rocks that cooled slowly (deep in the crust). The small crystals are found in rocks that have cooled quickly on the surface.
- Plutonic igneous rocks are formed when magma cools within the earth's crust. eg. granite.
- Volcanic igneous rocks are formed when molten rock cools and hardens on the surface. eg. basalt.
- Formed from magma deep within fold mountains(destructive boundaries).
- Maga raises to the buckled and folded rock to form batholiths.
- This maga cools very slowly to create crystals of mica, feldspar and quartz (these three materials form granite).
Formation of Basalt - Volcanic Rock
- Basalt is formed when magma is cooled quickly on or near the surface.
- Basalt is a dark heavy rock and may have rusty spots because of its high iron content.
Sedimentary Rocks
- Sedimentary rocks form from sediments of other rocks which have been weathered and eroded.
- These sediments are compressed and compacted in layers.
- Examples of organic sedimentary rocks: Coal and limestone.
- Examples of non-organic sedimentary rocks: Sandstone and shale.
Metamorphic rocks
- Metamorphic rocks are rocks that have been changed from igneous and sedimentary rocks due to heat and/or pressure. This process is called metamorphism.
- These rocks are formed where plates collide.
- Compression and collision of the plates creates heat and pressure.
- Limestone is changed to marble.
- Sandstone changed to quartzite.
- Shale changed to slate or schist.
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Human Interaction with Rocks -Essay
Human Interference with Rocks:
- Natural Gas Natural gas is formed in sedimentary rocks. Plants and animals decay, then are buried under sand and Mud where there is little oxygen.
- The pressure and bacteria break this material down into gas. The gas becomes trapped in between the layers of permeable rock.
- Natural gas generates revenue and creates employment. The world Oil and Gas Industry is worth approximately €186 billion.
- Gas is the cleanest and most efficient of all the fossil fuels. However digging and drilling for pipes can damage the surrounding environment.
- Natural gas is 25% of energy use in Ireland. Ireland uses 1% of the total European production.
- Gas is used in electricity Generation by the ESB and is also used in the Industrial sector and by more than half a million homes.
- The gas is found by using small explosions to create seismic waves.
- Kinsale is Ireland's main gas field which was discovered in 1971 and began production in 1978. It is piped into cork Harbour.
- It is located 1 kilometre below the seabed on 100 metres of water.
- Gas was later found at "Seven Heads" but the flow was much lower than expected. The gas reserves at these two Fields, is almost gone.
- More gas was found at the Corrib Gas-field 70 kilometres off the coast of Mayo.
- It is 3500 metres below sea bed on 300 metres of water and is approximately two thirds the gas levels at Kinsale.
- It is piped into cork Harbour.
- This is a very controversial gas field and many protests have been held. This has delayed the opening of the gas field.
- It was originally hoped that the gas would have been pumped by 2006 but it only started pumping in 2015.
- Bord Gais is responsible for the gas pipeline but has been open to competition in recent years. 2 Subsea gas pipelines were built between Dublin and Scotland.
- Corrib gas will also attract industry to the peripheral region of the West of Ireland. The government offers attractive terms to encourage oil and gas exploration.
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Rock Quiz
- What is a mineral?
- Name the 3 categories of rock. (3)
- What is another name given to intrusive rock?
- What is another name given to extrusive rock?
- What does lithification mean?
- What is strata?
- What is the most common rock in Ireland.
- What 3 minerals make up Granite? (3)
- What is denudation? (2)
- What landform is created at a fissure eruption?
- How many yrs ago was the Giant's Causeway formed?
- What shape are the columns?
- Name 3 categories of sedimentary rock. (3)
- What does ORS mean and what mineral is responsible for this name. (2)
- Where can ORS be found?
- What name is given to rough sedimentary rock containing large pebbles?
- Why is limestone grey?
- What orogeny took place 400mya?
- What does "metamorphic" mean?
- What is another name for contact metamorphism? Why is it called this? (2)
- When/where does regional metamorphism occur?
- What rock was marble before it came into contact with great heat or pressure?
- What is the name given to the famous pure white marble from Italy?
- Serpentine and Iron Oxide change marble to which 2 colours? (2)
- Quartzite is made from which rock?
- It remains as a resistant cap of which 2 famous mountains in Ireland? (2)
- What is an active plate margin? Give an example (3)
- What are the main processes at a trailing margin? Give an example (3)
- Give one use for each rock we have studied. (6)
- What does permeable mean?
- How much is the oil and gas industry worth?
- What % of energy in Ireland comes from natural gas?
- How is gas found?
- Which of the 2 gas fields in Ireland was exploited first?
- What delayed the 2nd gas field from opening? (2)
- Who is responsible for natural gas in Ireland?