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6th Grade  Chapter 15 Part 2
 

6th Grade Chapter 15 Part 2

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    6th Grade  Chapter 15 Part 2 6th Grade Chapter 15 Part 2 Presentation Transcript

    • Chapter 4 Rocks
    • The Rock Cycle H.W. pg. 93 ques. 1-4
      • A rock is a mixture of minerals, rock fragments, volcanic glass, organic matter, and other natural materials.
      • All rocks slowly change through time, and the model that we use to show this slow change is called the rock cycle .
    • Rock Cycle
      • As you can see the rock cycle shows 3 different types of rock:
      • Sedimentary
      • Metamorphic
      • Igneous
      • Also you see that all 3 types can be formed in a number of ways.
      • This shows that any rock can change into any of the three major rock types.
    • Igneous Rock
      • Igneous rock forms when magma cools and hardens.
      • At certain within the Earth, the temperature and pressure are just right for rocks to melt and form magma.
      • Magma can be located at depths of 150km below the Earths surface. The temperature of this magma can range between 650- 1,200 o C, depending on their chemical compositions and pressures exerted on them.
    • Igneous Rock
      • The reason that these rocks melt is because of heat that is formed in the Earth’s interior.
      • The heat comes from the decay of radioactive material inside the Earth.
      • Another source of this heat is actually heat that is left over from the formation of the planet, which was originally molten.
      • Since magma is less dense than the surrounding rocks it is forced upward toward the surface, like in a volcano.
      • When magma reaches the Earths surface and flows from volcanoes it is then called lava
    • Igneous Rock
      • So magma is melted rock material composed of common elements and fluids.
      • As magma cools atoms and compounds rearrange themselves into new crystals called mineral grains . And rocks form as these mineral grains grow together.
      • So rocks that form from magma below the Earths surface are called intrusive.
      • These intrusive rocks stay underground until the land above them are removed, either by erosion of by physical means, and exposed to the surface.
    • Igneous Rock
      • Intrusive rocks form at deep depths of the Earth. This causes the rocks to cool very slowly.
      • Slowly cooled magma will then produce very large mineral grains that we can see, within the intrusive rocks.
    • Igneous Rock
      • Extrusive igneous rocks are formed by the cooling of lava on the surface of the Earth.
      • When lava cools on the surface it could be exposed to water and air. This causes the lava to cool quickly and does not allow large mineral grains to form.
      • Therefore extrusive igneous rock looks fine grained.
    • Metamorphic Rock
      • Rocks that have changed because of changes in temperature and pressure or the presence of hot, watery fluids are called Metamorphic Rock.
      • These changes can be in the form of the rock or in its composition or both.
      • Metamorphic rocks can form from igneous, sedimentary or from other metamorphic rocks.
      • Ex: When you add heat and pressure to granite, the mineral grains are flattened and a metamorphic rock called gneiss is formed.
    • Granite & Gneiss
    • How to Classify Metamorphic Rock
      • Metamorphic rocks can form from igneous, sedimentary, or other metamorphic rocks through their interaction with heat pressure and hot fluids.
      • We classify these rocks by their composition and texture.
      • First is Foliated rocks . A metamorphic rock is said to have foliated texture when mineral grains in the rock line up in parallel layers.
    • Metamorphic foliated rock
      • Two examples of foliated rocks are slate and gneiss.
    • Non Foliated metamorphic Rock
      • In non foliated metamorphic rock layering does not occur. The mineral grains grow and rearrange but do not form layers.
      • This produces a non foliated texture.
      • An example is when sandstone, a sedimentary rock composed of mostly quartz grains, is exposed to heat and pressure.
      • The quartz grains here grow in size and become interlocking like a jigsaw puzzle.
      • The resulting rock is called quartzite.
    • Non Foliated metamorphic Rock
    • Sedimentary Rock
      • Igneous rocks are the most common rocks on Earth. However we don’t see them a lot because they are mostly beneath the Earths surface.
      • 75% of the rocks that are exposed at the surface are sedimentary rocks .
      • Sediments are loose materials such as rock fragments, mineral grains, and bits and pieces of shell that have been moved by wind, water, or ice
      • These sediments come from already existing rock that were weathered or eroded.
      • Sedimentary rock forms when these sediments are pressed together by great pressure, or when minerals form in solution.
    • Stacked Rocks
      • Sedimentary rocks often form in layers. The older layers are on the bottom layers because they were deposited first.
      • Sometimes these layers can be disturbed by the forces of nature. This will sometimes overturn the layered sedimentary rock and the oldest will no longer be on the bottom.
    • Conglomerate
      • Test on chapter 3 in one week!!!!!!!!!!!!!
      Test in One Week!!!!!