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  • 1. Explain to your partner how igneous rocks are formed.
  • 2. 8H Rock factory A volcano is a giant rock factory. Magma (molten rock) from below the ground is pushed to the surface and cools. The rock that forms is called igneous rock.
  • 3. Investigation of the Formation of Crystals in Rocks
    • Learning Objectives :
    • To know that igneous rocks crystallise from magma.
    • To be able to explain that the rate of cooling and crystallisation determines the size of the crystals in igneous rock.
    • To be able to conclude where certain igneous rocks would have formed around a volcano.
  • 4. Investigation of crystallisation
    • Experiment 1
    • Warm a glass slide to around 50  C and use a glass rod to spread some molten salol onto the slide. Then leave it to cool slowly on a heat-proof mat (see top diagram on the right).
    • Experiment 2
    • Prepare a glass slide as before and then place it onto a chilled aluminium tray. Place the tray and slide into a freezer, or on to a large beaker containing ice (see bottom diagram on the right).
  • 5. Practical Activity
    • Safety First:
    • Wear safety goggles
    • Stand up
    • Tuck your chair & bags under your desk
    • Tie back long hair
  • 6. Prepare a TV News Report
    • You are going to be interviewed on TV about the formation of crystals in igneous rocks and how they are affected by temperature.
    • You need to describe your demonstration to show why crystal sizes in igneous rocks vary. Briefly state your results and explain how these led you to reach your conclusions.
  • 7. Example:
    • Scientists have made a major break-through in their understanding of the structure of the Earth. Careful observation and recording of data has enabled a leading team of scientists to describe how granite was formed and why different pieces of granite have different sized crystals in them. We interviewed one of the scientists who said …
  • 8. Formation of igneous rocks magma intrusive igneous rock extrusive igneous rock Igneous rocks are formed when magma cools and solidifies. How are igneous rocks formed? Deep in the ground is molten rock called magma . Sometimes, magma bursts through the surface causing volcanic eruptions.
    • When magma cools above the surface, extrusive igneous rocks are formed.
    • When magma cools below the surface, intrusive igneous rocks are formed.
  • 9.
    • How is the size of crystals in igneous rocks determined by the rate at which magma cools and solidifies?
    Size of crystals in igneous rocks
    • Magma above the Earth’s surface cools quickly . Only small crystals are formed as the magma solidifies.
    • This is how extrusive igneous rocks like pumice and basalt are formed.
    • Magma below the Earth’s surface cools slowly . There is time for
    • large crystals to grow as the
    • magma solidifies.
    • This is how extrusive igneous rocks like granite are formed.
  • 10.  
  • 11. Explain how each rock was formed:
    • Rock A
    • Rock B
    In which state the particles in a rock could begin to move? Explain.
  • 12. Investigation of the Formation of Crystals in Rocks
    • Learning Objectives :
    • To know that igneous rocks crystallise from magma.
    • To be able to explain that the rate of cooling and crystallisation determines the size of the crystals in igneous rock.
    • To be able to conclude where certain igneous rocks would have formed around a volcano.