Igneous Rocks 30 Flashcards
Where are igneous rocks formed
Constructive and destructive plate boundaries
Name the two types of igneous rocks and where in Ireland
Intrusive - granite (Wicklow mountains)
Extrusive - Basalt (Giants causeway Co.Antrim)
How is granite is formed and example
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
Where in the plate does granite form
Several kilometres below surface
Magma from the mantle cools deep under ground
Colour and crystal size of granite
Grey pink white
Big crystals
What colour granite is most common in Ireland
Grey
What are the crystals in granite made up of
Quarts
Mica
Feldspar
When was granite formed in Ireland
400 mill ago during Caledonian mountain building
Magma chambers formed under surface and cooled slowly to form granite
What is an intermediate granite rock
When magma cools closer to the surface
It cools faster and smaller grained rocks are formed (eg Dolerite Fairhead Co.Antrim)
Where can intermediate rock be found in Ireland
Dolerite
Fair head Co.Antrim
Name an intermediate and plutonic
I - dolerrite
P - granite
What do intermediate and plutonic rocks have in common
They are both acidic igneous rocks and contain more than 55% silica
What is granite used for
Building and countertops because it is very strong and resistant to erosion and weathering
What happens when granite is exposed to rainwater
It breaks up to form clay
How is the sugar loaf in Wicklow formed (Granite)
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
Name an extrusive rock
Basalt
How are basalt rocks formed
> 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
What is an obsidian rock
Smoother rock with tiny crystals and a glassy texture (extrusive)
What is basalt used in
Road contruction
Resistant to weathering and erosion
When was the Giants causeway formed and how
60 million years ago
Lava cooled quick in a stream of water causing basalt to shrink and contract into hexagon chapped columns
What happens when basalt is weathered
It forms a deep fertile soi(eg fertile river valleys of ulster)
Where in the world is basalt currently forming
Iceland at the mid- Atlantic ridge
How are basalt domes formed
Acidic lava (more than 55% silica) does not flow across surface easily Basalt domes often form in this case (eg Mount St. Helens,America)
Example of a basalt dome
Mount St. Helens America
What is subduction
When an oceanic plate slides beneath a continental plate, melts and is recycled
Magma rises into continental plate and cools slowly
