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Igneous Rock Inside the Restless Earth Chapter 2, Section 2 6th Grade Mrs. Boguslaw

6th Types of Rock - MRS. BOGUSLAW'S WEBPAGEIntrusive Igneous Rock • Rock formed from the cooling and solidification of magma UNDER the Earth’s surface • Usually cools slowly,

Aug 29, 2020



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  • Igneous RockInside the Restless Earth Chapter 2, Section 2

    6th Grade Mrs. Boguslaw

  • Igneous Rock• Always begins as magma

    • Magma can form when rock is heated, when pressure is released, or when rock changes composition

    • Because magma is made of many different melted minerals, some minerals become solid before others do

  • Composition and Texture of Igneous Rock

    • The longer it takes for magma or lava to cool, the more time mineral crystals have to grow

    • Longer time —> bigger crystals —> coarser texture

    • Less time —> smaller (or no) crystals —> finer texture

  • Intrusive Igneous Rock

    • Rock formed from the cooling and solidification of magma UNDER the Earth’s surface

    • Usually cools slowly, so has a coarse-grained texture with large crystals

  • Intrusive Igneous Rocks• Masses are named for sizes and shapes

    • Batholith: largest

    • Stock: smaller than batholiths

    • Dike: sheetlike, cut across other previous rock units

    • Sills: parallel to previous rock units

  • Extrusive Igneous Rock

    • Rock that forms as a result of volcanic activity at or near the Earth’s surface, cools ABOVE the surface of the Earth

    • Cools quickly, so usually fine grained with small or no crystals

  • Sedimentary RockInside the Restless Earth Chapter 2, Section 3

    6th Grade Mrs. Boguslaw

  • Sedimentary Rock

    • Forms at or near the Earth’s surface

    • Forms without the extreme heat and pressure needed for igneous and metamorphic rock

    • Most noticeable feature is strata - layers of rock

  • Origins of Sedimentary Rock• Wind, water, ice, sunlight, and gravity all cause rock to

    weather into fragments called sediment

    • Through erosion, this sediment is moved from one place to another

    • During deposition, the sediment is deposited in layers

    • As new layers of sediment are deposited, old layers are covered and compacted. Dissolved minerals form a natural cement that binds the sediment into sedimentary rock

  • Composition of Sedimentary Rock

    • Classified by the way it forms

    • Clastic sedimentary rock: made of fragments of rock cemented together by a mineral like calcite or quartz

    • Chemical sedimentary rock: forms from solutions of dissolved minerals and water; rainwater dissolves rock and then it re-crystalizes

    • Organic sedimentary rock: forms from the remains of once-living plants and animals; includes limestones and coal

  • Sedimentary Rock Structures

    • Most important feature is stratification

    • Stratification: the process in which sedimentary rocks are arranged in layers

    • Strata are different depending on kind, size, and color of sediment

    • Sedimentary rock can sometimes also show the motion of wind or water, called ripple marks

    • Mud cracks can show areas that once had water that has dried up, like ancient lakes, streams, or shoreline

  • Metamorphic RockInside the Restless Earth Chapter 2, Section 4

    6th Grade Mrs. Boguslaw

  • Origins of Metamorphic Rock

    • The texture or mineral composition of a rock can change when its surroundings change

    • If the temperature or pressure of the new environment is different from the one in which the rock formed, it will undergo metamorphism

  • Origins of Metamorphic Rock

    • Contact Metamorphism

    • Heated by nearby magma

    • Does not melt the rock

  • Origins of Metamorphic Rock

    • Regional Metamorphism

    • Occurs when pressure builds up deep below other rock formations or when large pieces of the Earth’s crust collide

    • Increased temperature and pressure causes rock to become deformed and chemically changed

  • Composition of Metamorphic Rock

    • Metamorphism occurs when temperature and pressure inside the Earth’s crust change

    • Minerals that were present when the rock first formed might not be stable in the new temperature and pressure conditions, so they change into more stable minerals

    • Index minerals are minerals that form only at certain temperatures and pressures. They help us estimate the temperature, pressure, and depth at which a rock undergoes metamorphism

  • Textures of Metamorphic Rock

    • Either foliated or non foliated

    • Foliated Metamorphic Rock

    • Mineral grains are arranged in planes or bands

    • As heat and pressure increases, metamorphism continues

  • Textures of Metamorphic Rock

    • Nonfoliated Metamorphic Rock

    • Mineral grains are NOT arranged in planes or bands

    • Commonly made out of one or only a few minerals

    • Crystals change in size and composition during metamorphism

  • Metamorphic Rock Structures

    • Deformation: a change in the shape of a rock caused by a force placed on it

    • Folds or bends in rock are structures that indicate that a rock has been deformed