Chapter 5: The Rock Cycle Plutonic rocks • Formed within the Earth • Intrusive • e.g. granite
Dec 23, 2015
Chapter 5: The Rock Cycle
Plutonic rocks
• Formed within the Earth
• Intrusive
• e.g. granite
Chapter 5: The Rock Cycle
Volcanic rocks
• Formed at the surface of the Earth
• Extrusive
• e.g. basalt
Chapter 5: The Rock Cycle
The rock cycle
• Rocks continually form, change, are destroyed and reconstituted
• Endogenic forces – construct and modify
• Exogenic forces – destroy
• Deposition – reconstitute
Chapter 5: The Rock Cycle
Magma
• Rock layers subduct into the crust and mantle
• Rock layers melt and form molten rock
Chapter 5: The Rock Cycle
Rocks vary in their:
• Origin
• Formation
• Characteristics
Chapter 5: The Rock Cycle
Three major rock groups exist:
• Igneous
• Sedimentary
• Metamorphic
Chapter 5: The Rock Cycle
Rock Formation
1. Igneous
• Magma rises, cools and solidifies to form igneous rocks
• Magma reaches the surface, it forms volcanic rock
• Magma cools and hardens within the crust, it forms plutonic rock
Chapter 5: The Rock Cycle
Rock Formation (continued)
2. Sedimentary• Destroyed where denudation occurs on the
surface
• Weathering
• Erosion
• Break down into sediments
• Sediments are then deposited and compressed
Chapter 5: The Rock Cycle
Rock Formation (continued)
3. Metamorphic
• Modified due to either great heat or pressure or both
Chapter 5: The Rock Cycle
Characteristics of the different types of rocks
1. Igneous rock
Two types:
I. Plutonic or intrusive rocks
• Formed when magma cooled down and solidified inside the Earth’s crust
• e.g. granite
II. Volcanic and extrusive
• Formed when lava cooled and solidified on the Earth’s surface or close to the surface
• e.g. basalt
Chapter 5: The Rock Cycle
Igneous rocks contain crystals
• Size tells length of time it took rock to cool
• Large crystals cooled slowly within the Earth’s crust
• Small crystals, cooled quickly on the Earth’s surface
Chapter 5: The Rock Cycle
Granite
• Coarse-grained
• Formed when magma cooled deep within the Earth’s crust
• Contains minerals of feldspar, quartz and mica
• Varies in colour – white, grey, pink or black
• Crystals are large, the rock cooled slowly
• e.g. Wicklow Mountains
Chapter 5: The Rock Cycle
Basalt
• Fine-to-medium-grained
• Ranges in colour – black to dark grey
• Formed when lava cooled quickly on the Earth’s surface
• Small crystals
• e.g. Antrim-Derry Plateau
• Giant’s Causeway
• Six-sided columns, hexagonal in shape
Chapter 5: The Rock Cycle
Characteristics of the different types of
rocks
2. Sedimentary rock
• Formed over millions of years
• Rock fragments and the remains of animals and plants compressed under pressure to form solid rock
• e.g. limestone and sandstone
Chapter 5: The Rock Cycle
Two types of sedimentary rock
i. Inorganic sedimentary rock
• Inorganic sedimentary rock formed from the broken down remains of pre-existing rock
ii. Organic sedimentary rock
• Organic sedimentary rock formed from the remains of animal and plant life
Chapter 5: The Rock Cycle
Limestone
• Organic sedimentary rock
• Most common type of rock in Ireland
• Cemented and compressed remains of fish and other sea creatures
• Over millions of years compressed and formed slowly into solid rock
• Carboniferous period
• Contains calcium carbonate
• Varies in colour - greyish white, black, dark grey
• e.g. the Burren in Co. Clare
Chapter 5: The Rock Cycle
Sandstone
• Inorganic sedimentary rock
• Coarse
• Usually brown or red
• Formed approximately 400 million years ago
• Sediments laid down in layers
• Each successive layer compressed the next layer
• Cemented to form sandstone
• e.g. Comeragh Mountains, Co. Waterford
Chapter 5: The Rock Cycle
Characteristics of the different types of
rocks
3. Metamorphic rock
Formation:
• Sedimentary or igneous rocks changed by either great heat or pressure (or both)
• Magma
• Folding
• Appearance, texture and chemical composition change
Chapter 5: The Rock Cycle
Types of metamorphism
i. Thermal
• heat alone
• rocks change in composition
ii. Regional
• great heat and pressure over a large area
• fold mountain
• colliding plates
• rising magma
Chapter 5: The Rock Cycle
Examples of sedimentary rock changing into
metamorphic rock
• Limestone changes to marble, e.g. Connemara in Co. Galway
• Sandstone changes to quartzite, e.g. Sugarloaf Mountain, Co. Wicklow
Chapter 5: The Rock Cycle
Marble
• Metamorphic rock
• Limestone
• Heat and pressure
• Various colours
• Connemara (green)
• Kilkenny (black)
• Cork (red)
• Rathlin Island, Antrim and Carrara, Italy (white)
Chapter 5: The Rock Cycle
Quartzite
• Metamorphic
• Sandstone
• Heat and pressure
• Mountain building
• Sandstone came into contact with magma
• Light-coloured rock, e.g. Croagh Patrick, Co. Mayo
Chapter 5: The Rock Cycle
Active plate margins
• Oceanic plate subducting under a continental plate
• Faulting, mountain building, volcanoes and earthquake activity
• e.g. west coast of North America Pacific plate subducting under North American plate
Chapter 5: The Rock Cycle
Trailing plate margin
• Absence of earthquake, volcanic activity or folding
• Sedimentary rocks form, e.g. sandstone and limestone
Chapter 5: The Rock Cycle
Quarrying case study
• Important resource
• Energy
• Building materials
Chapter 5: The Rock Cycle
1. Methods of quarrying
I. Plug and feather
• drilling holes
• split the rock
• extracting large pieces, e.g. floor covering
II. Explosive
• extracting large and small pieces of rock
III. Channelling
• machinery cuts large slices of rock
• metamorphic rock such as marble
Chapter 5: The Rock Cycle
2. Positive impacts of quarrying
• Direct employment
• Construction
• Indirect employment
Chapter 5: The Rock Cycle
3. Negative impacts of quarrying
• Visual pollution
• Noise pollution
• Heavy machinery damage to infrastructure
• Dust pollution
• Water pollution
• Disused quarries
Chapter 5: The Rock Cycle
4. Carrara marble
• Tuscany, Italy
• White or blue-grey marble
• Used since the time of ancient Rome
• Statue of David – Michelangelo
• Exported all around the world
• Construction of buildings
• Warm countries
• Reflect light
• Create an air of coolness