Chapter 5: The Rock Cycle Plutonic rocks Formed within the Earth Intrusive e.g. granite.

Chapter 5: The Rock Cycle

Plutonic rocks

• Formed within the Earth

• Intrusive

• e.g. granite


Volcanic rocks

• Formed at the surface of the Earth

• Extrusive

• e.g. basalt


The rock cycle

• Rocks continually form, change, are destroyed and reconstituted

• Endogenic forces – construct and modify

• Exogenic forces – destroy

• Deposition – reconstitute


Magma

• Rock layers subduct into the crust and mantle

• Rock layers melt and form molten rock


Rocks vary in their:

• Origin

• Formation

• Characteristics


Three major rock groups exist:

• Igneous

• Sedimentary

• Metamorphic


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


Rock Formation (continued)

2. Sedimentary• Destroyed where denudation occurs on the

surface

• Weathering

• Erosion

• Break down into sediments

• Sediments are then deposited and compressed


Rock Formation (continued)

3. Metamorphic

• Modified due to either great heat or pressure or both


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


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


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


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


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


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


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


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


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


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


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


Marble

• Metamorphic rock

• Limestone

• Heat and pressure

• Various colours

• Connemara (green)

• Kilkenny (black)

• Cork (red)

• Rathlin Island, Antrim and Carrara, Italy (white)


Quartzite

• Metamorphic

• Sandstone

• Heat and pressure

• Mountain building

• Sandstone came into contact with magma

• Light-coloured rock, e.g. Croagh Patrick, Co. Mayo


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


Trailing plate margin

• Absence of earthquake, volcanic activity or folding

• Sedimentary rocks form, e.g. sandstone and limestone


Quarrying case study

• Important resource

• Energy

• Building materials


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


2. Positive impacts of quarrying

• Direct employment

• Construction

• Indirect employment


3. Negative impacts of quarrying

• Visual pollution

• Noise pollution

• Heavy machinery damage to infrastructure

• Dust pollution

• Water pollution

• Disused quarries


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

Chapter 5: The Rock Cycle Plutonic rocks Formed within the Earth Intrusive e.g. granite.

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Chapter 5: The Rock Cycle Plutonic rocks Formed within the Earth Intrusive e.g. granite.