In this section, you will learn: z how two types of igneous rock – basalt and granite – are formed
z the characteristics of basalt and granite and where they are found in Ireland
z how people interact with igneous rocks and use them to their advantage.
Basalt
Granite Extrusive Crystal
Hexagonal Intrusive
Basalt and granite are the two most common igneous rocks in Ireland. As we have already learned, igneous rocks are formed from volcanic activity.
Basalt Colour: Grey/black Texture: Medium grained
Formation: BasaIt is an extrusive rock. It is formed when lava spreads out over the surface of the Earth’s crust due to volcanic activity. It then cools and hardens. Basalt has tiny crystals which cannot be seen without the use of a microscope. This is because the lava cooled and hardened very quickly in the open air when it reached the surface.
Use: Basalt is used for road chippings due to its hardness. The landscape created by basalt can also be a tourist attraction.
Example: Basalt is found in the Antrim–Derry Plateau in the north-east of Ireland. The Giant’s Causeway is part of this plateau. As the lava there was so thick, when it cooled it contracted to form the hexagonal (six-sided) shapes that can be seen today.
Extrusive rock is formed above the surface of the Earth.
: Figure 3.3 Giant’s Causeway, Co. Antrim
Go to page 10 of your Portfolio to create an article about tourism and the Giant’s Causeway. PORTFOLIO ACT VITY 3.1
Granite Colour: Range of colours, including black, grey, pink and cream Texture: Coarse grained
Formation: Granite is an intrusive rock. It is formed when molten magma pushes its way into the crust and cools and hardens there, under the surface. Granite has large crystals. This is because the molten magma cooled very slowly over millions of years. Some of these crystals include the minerals quartz, feldspar and mica. Granite is eventually
