Please enable JavaScript.
Coggle requires JavaScript to display documents.
Physical Geography: The Rock Cycle - Coggle Diagram
Physical Geography: The Rock Cycle
Types of rock
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
Sedimentary
Destroyed where denudation occurs on the surface
Weathering
Erosion
Break down into sediments
Sediments are then deposited and compressed
Metamorphic
Modified due to either great heat or pressure or both
Characteristics of igneous rocks
Two types of igneous rock:
Plutonic or intrusive rocks
Formed when lava cooled and solidified on the Earth’s surface or close to the surface, e.g. basalt
Basalt
Fine to medium-grained
Ranges in colour – black to dark grey
Formed when lava cooled quickly on the Earth’s surface
Small crystals
Example: Antrim-Derry Plateau
Includes the Giant’s Causeway
Six-sided columns, hexagonal in shape
Volcanic or extrusive rocks
Formed when magma cooled down and solidified inside the Earth’s crust, e.g. granite
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
400 MYA Caledonian fold mountain period
Example: Wicklow Mountains
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
Characteristics of sedimentary rocks
Formed over millions of years
Rock fragments and the remains of animals and plants compressed under pressure to form solid rock
Examples: limestone and sandstone
Two types of sedimentary rock:
Inorganic sedimentary rock
Formed from the broken-down remains of pre-existing rock
Sandstone
Inorganic sedimentary rock
Coarse
Usually brown or red, old red sandstone
Formed approximately 400 million years ago
Sediments laid down in layers
Each successive layer compressed the next layer
Cemented to form sandstone
Example: Comeragh Mountains, Co. Waterford
Organic sedimentary rock
Formed from the remains of animal and plant life
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
Example: the Burren in Co. Clare
Characteristics of metamorphic rocks
Formation:
Sedimentary or igneous rocks changed by either great heat or pressure (or both)
Types of metamorphism:
Thermal metamorphism
Heat alone
Rocks change in composition
Regional metamorphism
Great heat and pressure over a large area
Fold mountain
Colliding plates
Rising magma
Examples of sedimentary rock changing into metamorphic rock
Limestone changes to marble, e.g. Connemara, Co. Galway
Metamorphic rock
Once limestone
Heat and pressure
Various colours
Connemara (green)
Cork (red)
Rathlin Island, Antrim and Carrara, Italy (white)
Sandstone changes to quartzite, e.g. Sugarloaf Mountain, Co. Wicklow
Metamorphic
Sandstone
Heat and pressure
Mountain building
Sandstone came into contact with magma
Light-coloured rock, e.g. Croagh Patrick, Co. Mayo
Magma
Folding
Appearance, texture and chemical composition change
Plate margins
Active plate margin
Oceanic plate subducting under a continental plate
Faulting, mountain building, volcanoes and earthquake activity
Example: west coast of North America, Pacific Plate subducting under North American Plate
Newest and youngest igneous and metamorphic rocks formed here
Trailing plate margin
Absence of earthquake or volcanic activity or folding
Sedimentary rocks form, e.g. sandstone and limestone
The rock cycle
Rocks are continually formed, changed, destroyed and reconstituted
Melting of rocks by internal forces, e.g. magma
Broken down by denudation and tectonic forces
Reformed by compaction and sedimentation
Human interaction with the rock cycle
Rocks are of economic importance to people
Case Study: Geothermal energy production
Renewable energy, cost effective, e.g. Iceland
Molten magma near surface heats underground water supply
Water superheated to 200°C
Wells drilled to extract water
Used to generate electricity
Used for central heating in 90 per cent of people’s homes
Used to heat greenhouses
Reykjavik uses clean fuel source, lowest CO2 levels
Tourism attracted to natural hot springs and pools
Cheap fuel source
Pumped under car parks to keep them ice free