Chapter 9

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Rocks of the Earth

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Chapter 9

  1. 1. Chapter 09 Rocks of the Earth
  2. 2. 1 Samuel 2:2 There is no one holy like the LORD, Indeed, there is no one besides You, Nor is there any rock like our God.
  3. 3. What Are Rocks? • Rocks are solid materials of the Earth’s crust • They are made of substances known as minerals and are formed in various ways • Landforms such as mountains and volcanoes are made up entirely of rocks • Geologists classify rocks into three types:  Igneous  Sedimentary  Metamorphic
  4. 4. Igneous Rocks • • Igneous rocks are molten material (called magma) that has cooled and solidified The texture of rock is affected by the speed at which magma cools and hardens: Coarse-grained igneous rocks are formed when magma cools and hardens inside the Earth Lava  If magma cools and hardens slowly, a coarse-grained rock results e.g. granite  If magma cools and hardens quickly, a fine-grained rock results e.g. basalt Fine-grained igneous rocks are formed when the lava cools and hardens on the Earth’s surface Magma
  5. 5. Sedimentary Rocks • Formation of sedimentary rocks  Weathering and erosion break down or wear down rocks into smaller pieces  These tiny pieces of rock, together with sand, clay and silt are called sediments  Sediments are eventually deposited into rivers and seas and form layers on river or sea beds  As the layers of sediments pile up, weight of the upper layers presses down the lower layers, causing the sediments to cement together and harden  These solid, hardened layers of sediment are called sedimentary rock The weight of top layers causes layers below to cement and harden to form sedimentary rocks
  6. 6. Sedimentary Rocks • Texture of sedimentary rocks depends on the size of the original sediment  If the size of the sediments is small, sedimentary rocks formed will be fine-grained Shale e.g. shale  If the size of the sediments is big, the rock will be coarse-grained e.g. conglomerate conglomerate
  7. 7. Sedimentary Rocks • Some sedimentary rocks are formed from the remains of animals and plants e.g. limestone • The main characteristic of sedimentary rocks is that they are formed in layers which vary in thickness and appearance A limestone cave
  8. 8. Metamorphic Rocks • • • Metamorphic rocks are formed as a result of intense pressure and heat acting on igneous and sedimentary rocks This occurs due to crustal movements or when the rock comes into contact with molten magma Pressure and heat sometimes cause metamorphic rocks to have a foliated appearance (bands) e.g. slate Slate
  9. 9. The Rock Cycle - continual process of change in the rock types 2. Weathering and erosion of rocks result in sediments 1. Igneous rocks are formed from magma Igneous Rocks Sediments Magma 5. Metamorphic rocks that are buried deep in the Earth melt in the mantle Metamorphic Rocks 3. Large and small sediments pile up in layers, and are cemented and hardened to form sedimentary rocks 4. Under intense heat and pressure, sedimentary and igneous rocks change into metamorphic rocks Sedimentary Rocks

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