Unit 3
Rock, te rock cycle, and soil
3.1 Igneous rocks
❑ Find out that rocks can be classified into different types and describe the features of each
❑ Use diagrams and photographs to describe igneous rocks
❑ Describe the formation of igneous rocks in terms of magma and solidification
❑ Make predictions, based on what we know about how igneous rocks form
❑ Describe the accuracy of predictions, based on results
❑ Make a conclusion from results using science understanding
❑ Describe risks when planning practical work and carry out practical work safely
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❑Sort and group rocks by observing differences
❑Complete a key to igneous rocks based on easily observed differences.
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Getting started
1. Name the layers A, B, C and D.
2. What does layer B consist of ?
3. What happens when the material in layer B is ejected through the Earth’s surface?
B
C
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1. Name the layers A, B, C and D.
2. What does layer B consist of ?
3. What happens when the material in layer B is ejected through the Earth’s surface?
A Earth’s crust
B mantle
C Outer core
D Inner core
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2. What does layer B consist of ?
Magma
3. What happens when the material in layer B is ejected through the Earth’s surface?
A volcanic eruption occurs.
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Vocabulary for this lesson
Crystal Crystalline Extrusive igneous rock
geologist igneous rock
Intrusive igneous rock mineral
naked eye sedimentary rock solidification
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Rocks are different
Rocks differ from one another because they were formed in different ways.
Geologists are scientists who study rocks.
In the next few topics, you are going to be a geologist.
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Think like a scientist 1
Collect and sort rocks
1. Find some samples of rock. Make sure you don’t choose ‘manufactured’ materials like
concrete and brick. Good places to look are rock cuttings where a road passes through and the
rocks are exposed, or a quarry where rock is being cut out to use for building materials. Ask
on older sibling or adult to help you.
Safety: Be careful not to fall or climb any steep rock faces!
2. Put a label on each rock with your name and the place where you found the rock. Bring your
rock samples to class.
3. Work in groups and use a hand lens to study your rocks.
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4. Investigate your rocks by answering these questions about each rock:
a. Does the rock have only one color or different colors?
b. Does the rock consist of grains stuck together?
c. Can you see shiny crystals in the rock?
5. Divide your rocks into two groups:
❖Rocks which are one main color and consist of grains stuck together. These are sedimentary rocks. You
will find out more about them in the next topic.
❖Rocks which have shiny crystals and may have several color and a spotted appearance. These could be
igneous rocks. We will focus on igneous rocks in this topic.
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What are igneous rocks?
The word ‘igneous’ means fire.
Igneous rocks come from magma that has cooled into solid rock. Magma is hot, like a fire.
Look at the diagram. Notice that magma is coming from the mantle, deep below the
Earth’s surface. When magma cools it turns into a solid.
This process is called solidification.
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Some of the magma comes out at the surface as lava.
When the lava cools, it solidifies into an extrusive igneous rock.
‘Extrusive’ means outside the Earth’s crust on the surface.
The rock is a black rock called basalt.
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Some of the magma stays inside the Earth’s crust.
It cools down more slowly than the lava and solidifies into an intrusive igneous rock.
‘Intrusive’ means inside the Earth’s crust.
An example of an intrusive igneous rock is granite. On the diagram you can see that when
the rocks above the intrusive igneous rock wear away, the granite appears at the surface.
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What are igneous rocks made of?
All igneous rocks are made of minerals.
Each mineral consists of a different group of substances.
The most common substances in the Earth’s crust are silica, oxygen, aluminium,
magnesium and iron.
These substances join in different combinations to form minerals.
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The most important characteristic of all igneous rocks is that they are crystalline.
Crystals are formed when the minerals cool down.
Look at the photograph of quartz crystals.
Quartz is a mineral made up of silica and oxygen.
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When the magma is deep below the surface of the Earth it cools slowly.
This causes the crystals to form slowly.
The crystals are large enough for us to see with the naked eye.
But because the crystals are so close, they do not form shapes like the crystals on their
own in the photograph of quartz crystals.
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Look at the photograph of a piece of granite.
Notice that the rock has different colors because of the different crystals.
The minerals in granite are quartz, feldspar and mica.
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The lava cools quickly to form an extrusive igneous rock.
The crystals in the rock are too small to see with the naked eye.
An example is basalt.
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Describe igneous rocks and complete a key
1. Name the process where magma cools down and becomes a rock.
2. Do you think the magma that made granite rock cooled down slowly or quickly?
Explain your answer.
3. Is granite an extrusive igneous rock or an intrusive igneous rock?
4. Do you think the liquid basalt rock cooled down slowly or quickly?
Explain your answer.
5. Is basalt an extrusive igneous rock or an intrusive igneous rock?
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6. In the granite in the photograph:
a. Which mineral appears as glassy crystals?
b. Describe the crystals of feldspar.
c. Name the mineral which forms black, shiny crystals.
7. Copy and complete this key for igneous rocks:
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1. Name the process where magma cools down and becomes a rock.
Solidification.
2. Do you think the magma that made granite rock cooled down slowly or quickly?
Explain your answer.
Slowly, because the crystals are large enough to see with the naked eye.
3. Is granite an extrusive igneous rock or an intrusive igneous rock?
Intrusive igneous rock.
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4. Do you think the liquid basalt rock cooled down slowly or quickly?
Explain your answer.
Quickly, because the crystals are too small to see with the naked eye.
5. Is basalt an extrusive igneous rock or an intrusive igneous rock?
Extrusive igneous rock
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6. In the granite in the photograph:
a. Which mineral appears as glassy crystals?
Quartz
b. Describe the crystals of feldspar.
White and larger than the other crystals.
c. Name the mineral which forms black, shiny crystals.
Mica
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7. Copy and complete this key for igneous rocks:
Left granite right extrusive
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