Igneous Rocks As shown in figure 2, igneous rocks are formed from the magma found in the mantle just below the crust. When magma is forced up into the crust and becomes trapped, it begins to cool very slowly. Rocks formed in this way are known as intrusive igneous rock. Igneous rocks that form when lava reaches the earth’s surface are called extrusive. As the lava spreads out on the surface and meets the air, it cools and hardens very quickly.
Granite
Granite is an intrusive igneous rock. As it cooled very slowly over millions of years, the minerals in the magma formed very large crystals. These crystals include quartz, mica and feldspar.
Granite is multi-coloured. It is used in building monuments and gravestones, kitchen countertops and fireplaces. It can be found in the Dublin–Wicklow and Mourne Mountains.
Basalt
Basalt is an extrusive igneous rock. It cools very quickly when lava reaches the surface. Basalt has very small crystals that can only be seen using a microscope because it cools so fast.
Basalt is grey to black in colour. Crushed basalt is used in road building.
Basalt can be found in the Antrim–Derry plateau. The Giant’s Causeway in Antrim consists of columns of basalt.
Intrusive igneous rock Granite A granite counter top Igneous rock formation
Extrusive igneous rock
Key Words
Crystals Strata
Deposits
Permeable Soluble
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The world-famous Giant’s Causeway in Antrim
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Rocks
Fun Fact!
The Giant’s Causeway is Northern Ireland’s most popular tourist destination.
