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Year 8

Igneous rock

I can explain how igneous rocks form and describe features of different types.

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New
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Year 8

Igneous rock

I can explain how igneous rocks form and describe features of different types.

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Share activities with pupils
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Lesson details

Key learning points

  1. The melting point of rock is very high.
  2. Melted rock is called either lava (on Earth's surface), or magma (underground).
  3. Extrusive igneous rock forms outside Earth's crust, while instrusive igneous rock forms inside the crust.
  4. Some substances form crystals when they freeze.
  5. Crystal size depends on the rate at which melted rock cools.

Keywords

  • Lava - Molten (i.e. melted) rock that has broken through Earth's crust.

  • Magma - Molten (i.e. melted) rock beneath the Earth's surface.

  • Crystallisation - A process in which solid crystals form as molten rock cools.

  • Extrusive - A type of igneous rock that form when lava has cooled and crystallised; they form above Earth's surface.

  • Intrusive - A type of igneous rock that form when magma has cooled and crystallised; they form under Earth's surface.

Common misconception

Some think all lavas/magmas are the same and the type of igneous rock formed depends on cooling rate.

Stress that the type of igneous rock formed depends upon the mineral composition of the lava/magma *and* the rate of cooling. Use examples to reinforce this.

Handle the microscope slides minimally and only on the edges to maximize crystal formation during the salol practical. Leaving the slides on black card helps to see the crystals more clearly too.
Teacher tip

Equipment

Per group: melted salol, dropping pipette, 2 × cold microscope slides (kept in freezer), 2 × warm slides (kept in 45°C water bath/oven prior to use), hand lenses, optional extra – A5 black card.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
What are the key components that make up rocks?
plastic
water
Correct answer: fossils
Correct answer: shells
Correct answer: crystals
Q2.
Match the following rock types with their descriptions.
Correct Answer:igneous rocks,contain crystals that point in many directions

contain crystals that point in many directions

Correct Answer:sedimentary rocks,contain grains that are stuck together and may contain fossils

contain grains that are stuck together and may contain fossils

Correct Answer:metamorphic rocks,contain large crystals that all line up

contain large crystals that all line up

Q3.
A mineral is a substance with a crystal structure, while a rock consists of one or more minerals or rock fragments.
Correct Answer: pure
Q4.
Which of the following is evidence that supports the idea of tectonic plates moving?
Correct answer: volcanic eruptions and rock formations
lightning storms and wind patterns
ocean tides and river flows
cloud formations and rainfall
Q5.
rocks have spaces between grains, allowing water to pass through.
Correct Answer: porous
Q6.
Which of the following features is commonly found in igneous rocks?
fossilised leaves
aligned crystals
Correct answer: randomly oriented crystals
layered grains

Exit quiz

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6 Questions

Q1.
Which of the following is the correct name for molten rock that has broken through Earth's crust?
magma
Correct answer: lava
intrusive
extrusive
Q2.
Which of the following is a type of igneous rock that forms inside Earth's crust?
extrusive
Correct answer: intrusive
lava
magma
Q3.
Which of the following factors determines the size of crystals in igneous rocks?
the type of minerals present
Correct answer: the rate at which the molten rock cools
the depth of the magma
the type of tectonic plate boundary
Q4.
Sort the following steps into the correct order to describe how the melting of rock at the edge of a tectonic plate leads to the formation of extrusive igneous rock (e.g. basalt).
1 - Some rock at the edge of a tectonic plate could melt.
2 - It becomes magma.
3 - Magma can break through Earth’s surface at a volcano.
4 - It becomes lava.
5 - Lava cools quickly on the surface.
6 - It forms rock with crystals.
7 - The crystals are usually very small.
Q5.
Which of the following is an example of an intrusive igneous rock?
basalt
sandstone
marble
Correct answer: granite
Q6.
is the process in which solid crystals form as molten rock cools.
Correct Answer: crystallisation