Science at key stage 3 (Year 8)
Unit 8G: Rocks and weathering
Section 1: What are rocks made of?
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Objectives |
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- that rocks are usually made up of a mixture of mineral grains
- that two main textures can be recognised
- how to use experimental evidence and models to explain the texture of different rocks
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Activities |
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Outcomes |
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Children: |
- Show pupils samples of rocks and ask them to sort them into groups. Ask them to explain the basis for their groups, prompting if necessary by asking questions,
eg What makes the rock shiny? What can you see in the rock? Is the rock all the same colour? Ask pupils to record key responses. Discuss with them the words/observations that occurred most frequently.
- Provide pupils with samples of granite and sandstone and ask them to explore their textures,
eg by close observation using a magnifier and by immersion in water. Ask pupils to explain why one rock produces bubbles in water and the other does not. Investigate the absorption of water by weighing samples before and after immersion to illustrate porosity. Model interlocking and non-interlocking textures,
eg using a three-dimensional block puzzle and marbles, and relate observations to interlocking and non-interlocking textures. Ask pupils to record and explain their findings using annotated drawings and diagrams. Establish the idea that rocks are almost always mixtures of materials.
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- describe rocks as containing different grains which fit together
- explain that some grain shapes are interlocking and some are not,
eg some grains fit together and others do not; when the grains don't fit there are spaces and the water goes into these
- relate evidence about porosity to the way in which grains fit together
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Points to note |
- Rocks need to be chosen so that pupils will see easily that they are a mixture of different grains. The word most commonly used in their explanations/descriptions may be 'bits'.
- Some pupils may not realise that the term 'rock' as used by geologists includes unconsolidated material, such as sand, clay and peat, as well as harder materials.
- Differences between mixtures and chemical compounds are considered in unit 8F 'Compounds and mixtures'.
- It may be helpful to illustrate porosity using sponges of different kinds.
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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