2.5.3

Igneous Rocks

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Igneous Rocks

Igneous rocks are formed from cooling magma. They can either be formed inside the Earth’s crust or outside.

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Igneous rocks

  • Igneous rocks are formed from cooling magma.
  • There are two types of igneous rock: intrusive and extrusive.
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Features of igneous rock

  • They are very hard.
  • These rocks contain crystals.
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Intrusive igneous rock formation

  • Intrusive igneous rocks are formed inside the Earth’s crust.
  • They are formed from magma.
  • Because they form underground where it is hotter, they take a long time to cool.
  • This means the crystals that form are larger.
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Extrusive igneous rock formation

  • Extrusive igneous rocks are formed outside the Earth’s crust.
  • They are formed from lava from a volcanic eruption.
  • Because they form on the Earth’s surface where it is cooler, they take a short time to cool.
  • This means the crystals that form are smaller.
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Examples and their uses

  • Granite – used in building and tiles.
  • Basalt – used in construction and building roads.
  • Pumice – this floats on water because of air that was trapped when it cooled. Some people use this rock to remove the dead skin from their feet.
  • Obsidian – jet black in colour, this rock has been used for making tools and weapons such as arrowheads.

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1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Disciplinary Knowledge

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