Igneous Rocks 30

Question 1

Where are igneous rocks formed

Answer 1

Constructive and destructive plate boundaries

Question 2

Name the two types of igneous rocks and where in Ireland

Answer 2

Intrusive - granite (Wicklow mountains)

Extrusive - Basalt (Giants causeway Co.Antrim)

Question 3

How is granite is formed and example

Answer 3

Destructive plate boundary
Nazca plate meets South American plate
>Oceanic slides under continental 
>plate melts and is recycled 
>this magma rises into continental plate and cools slowly at a depth of several kilometres below the surface

Question 4

Where in the plate does granite form

Answer 4

Several kilometres below surface

Magma from the mantle cools deep under ground

Question 5

Colour and crystal size of granite

Answer 5

Grey pink white

Big crystals

Question 6

What colour granite is most common in Ireland

Answer 6

Grey

Question 7

What are the crystals in granite made up of

Answer 7

Quarts
Mica
Feldspar

Question 8

When was granite formed in Ireland

Answer 8

400 mill ago during Caledonian mountain building

Magma chambers formed under surface and cooled slowly to form granite

Question 9

What is an intermediate granite rock

Answer 9

When magma cools closer to the surface

It cools faster and smaller grained rocks are formed (eg Dolerite Fairhead Co.Antrim)

Question 10

Where can intermediate rock be found in Ireland

Answer 10

Dolerite

Fair head Co.Antrim

Question 11

Name an intermediate and plutonic

Answer 11

I - dolerrite

P - granite

Question 12

What do intermediate and plutonic rocks have in common

Answer 12

They are both acidic igneous rocks and contain more than 55% silica

Question 13

What is granite used for

Answer 13

Building and countertops because it is very strong and resistant to erosion and weathering

Question 14

What happens when granite is exposed to rainwater

Answer 14

It breaks up to form clay

Question 15

How is the sugar loaf in Wicklow formed (Granite)

Answer 15

As overlying sedimentary rocks are eroded away, harder igneous batholith of granite are exposed
Sugar loaf is coated with a ‘sprinkle’ of quartzite thus the name

Question 16

Name an extrusive rock

Answer 16

Basalt

Question 17

How are basalt rocks formed

Answer 17

> magma pushes through crust through fissures, mic ocean ridges and volcanoes from asthenosphere
lava cools once it is exposed to cooler temps and crystallisation will take place

Question 18

What is an obsidian rock

Answer 18

Smoother rock with tiny crystals and a glassy texture (extrusive)

Question 19

What is basalt used in

Answer 19

Road contruction

Resistant to weathering and erosion

Question 20

When was the Giants causeway formed and how

Answer 20

60 million years ago

Lava cooled quick in a stream of water causing basalt to shrink and contract into hexagon chapped columns

Question 21

What happens when basalt is weathered

Answer 21

It forms a deep fertile soi(eg fertile river valleys of ulster)

Question 22

Where in the world is basalt currently forming

Answer 22

Iceland at the mid- Atlantic ridge

Question 23

How are basalt domes formed

Answer 23

Acidic lava (more than 55% silica) does not flow across surface easily
Basalt domes often form in this case (eg Mount St. Helens,America)

Question 24

Example of a basalt dome

Answer 24

Mount St. Helens America

Question 25

What is subduction

Answer 25

When an oceanic plate slides beneath a continental plate, melts and is recycled
Magma rises into continental plate and cools slowly