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Natural sciences

The earth and beyond

Rock formations

Educator section

Memorandum

Igneous rock

1. cracks in the earth's crust

Key

2. earth's crust

3. lava cools and solidifies as grey / black basalt

4. red molten lava

5. crater of the volcano

6. magma forms lava

Assignment 5:

1. Magma (lava) will cool quickly as soon as it has erupted from the volcano and runs down the mountain slope

Reason: Little lava, exposed to the "cooler" atmosphere.

2. Granite is found deep underneath the crust

Reason: Magma has to cool slowly in order to form granite.

3. Deep underneath the earth's crust.

4. Deep underneath the earth's crust.

Reason: The surrounding rocks keep the magma hot for a very long time. Therefore, it cannot cool quickly.

5. Basalt is found on the slopes of the volcano.

Reason: Basalt forms when lava cools quickly. It has to be outside the crust.

6. The smallest crystals appear in basalt - thus on the mountain slopes and valleys near the volcano.

Leaner section

Content

WE ARE GOING TO STUDY THE DIFFERENT TYPES OF ROCK FORMATION

THAT FORM THE CRUST OF THE EARTH BECAUSE SEEDS DO NOT GROW EQUALLY WELL IN ALL KINDS OF SOIL.

  • Rocks, refers to the material that forms the earth's crust. Rock formations are grouped in three categories, namely igneous rocks, sedimentary rocks and metamorphic rocks.

Activity: to discuss igneous rocks as a type of rock formation [lo 2.1]

  • These rocks are the primary, original rock formation that made up the surface of the earth.
  • The earliest rock formations were igneous rocks that were formed when the planet started to cool down. The rocks are extremely hard and consist of several crystals.

Section through a volcano

KEY

1. ___________________________________________________________________

2. ___________________________________________________________________

3. ___________________________________________________________________

4. ___________________________________________________________________

5. ___________________________________________________________________

6. ___________________________________________________________________

We can work out how igneous rocks were formed by noting what happens to lava when there is a volcanic eruption. Lava cools down when it runs down the mountain slopes and begins to harden.

  • Basalt is formed after the eruption of a volcano. The lava cools down quickly, the crystals are small and the colour varies between dark grey and black. Sometimes the rock is perforated with small openings that are formed by small gas bubbles. This type of rock is used for pumice stone, which is used by people for rubbing off hardened dry skin on their feet.

  • The best-known rock formed from magma is granite. Granite is formed when magma cools down slowly below the surface of the earth. It is a very hard rock and mainly consists of white, black and cream-coloured crystals. The minerals in this type of rock are able to form larger crystals because the magma cools down so slowly.

ASSIGNMENT 5

Study the following diagram and answer the questions:

1. Where will the magma be able to cool down the soonest? Why?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(2)

2. Where do we find granite? Explain why.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(2)

3. Where will the largest crystals be found when the magma starts to harden?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(1)

4. Where will the magma cool down the slowest? Why?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(2)

5. Where will we find basalt? Explain why.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(2)

6. Where will the smallest crystals be found?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

(1)

Summative: 10

Assessment

Learning Outcome 2: The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

Assessment Standard 2.1: We know this when the learner recalls meaningful information.

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Source:  OpenStax, Natural sciences grade 6. OpenStax CNX. Sep 16, 2009 Download for free at http://cnx.org/content/col11079/1.1
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