1. 1A2 Geography 3rd March, 2015 Objective:
To introduce students to the formation of two types of igneous rock – basalt and granite.

2. Homework: Open your textbooks on page 92!
For Monday’s class, you must answer Q. 1 (i) & (ii).

3. Review During our last lesson, we learned that:
Rock is the hard substance that makes up Earth’s surface.
Rocks differ according to hardness, mineral content, colour, and texture.
All rocks are divided into one of three groups, according to the manner in which they are formed – igneous, sedimentary, and metamorphic.

4. Igneous Rocks Igneous rocks are formed from volcanic activity.
Hot molten magma cools down, either on the surface or within the crust.
Examples include granite and basalt.
“Igneous” derives from the Latin word for “fire.”

5. Igneous Rock Formation

6. Igneous Rock: Basalt
Basalt is an igneous rock that formed when lava spread out over the surface of the Earth’s crust and cooled and hardened.
Basalt contains crystals that are so small they cannot be seen without the use of a microscope.
Crystals are very small because the lava that formed the basalt cooled rapidly once it was exposed to the air.

7. Igneous Rock: Basalt Basalt is grey/black in colour.
It is medium grained in texture (neither very rough nor very smooth).
It can be found on the Antrim-Derry plateau. The Giant’s Causeway is part of this.
(Class on the Giant’s Causeway next week!)

8. Igneous Rock: Basalt
Uses for basalt include road chippings.

9. Igneous Rock: Granite
Granite was formed when magma filled weaknesses in the crust and cooled and hardened there.
The magma cooled slowly over of millions of years. As a result, large crystals formed. These include minerals such as quartz, feldspar and mica.
Granite is exposed to the surface when overlying rock is worn away.

10. Igneous Rock: Granite
Granite’s colour tends to vary according to the place in which it formed. It can be dark – grey and black – or light – cream and pink – in colour.
It is course grained (abrasive) in texture.

11. Igneous Rock: Granite
Examples of granite can be found in the east of Ireland in the Wicklow Mountains.
Granite has many uses. It is used very often in the construction industry. Kitchen worktops and fireplaces are sometimes made of granite, too.