Chapter 4 Rocks: Mixtures of Minerals

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Chapter 4Rocks Mixtures of Minerals

• Rocks A naturally occurring solid mixture of
  one or more minerals and organic matter.
• The Rock Cycle The continuous process by which
  new rock forms from pre-existing rock material.
  Rocks will actually change their chemical
  composition.
• Weathering The process in which wind, water,
  gravity and heat break down rocks to form
  fragments called sediment.
• Erosion The process in which sediments are
  washed or blown away from their source.
• Deposition The process in which eroded material
  is dropped and comes to rest.

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The Rock Cycle Activity

• Write a humorous story in your group about what
  it would be like to be a rock particle traveling
  through the rock cycle. Think of this as a story
  like The Little Grain That Could. Then you will
  present this as a group in class. The winning
  group gets 20 extra credit points!
• Magma partially or completely melted rock that
  forms igneous rock when it cools.

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The Classification of Rocks

• Composition The chemical make up of a rock.
  This describes the mineral composition of the
  rock.
• Texture The size, shape and position of the
  grains that make up the rock and determines its
  quality.
• Coarse Large grains
• Medium Smaller grains
• Fine Smallest grains. Almost cannot be
  seen.

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Igneous Rocks

• Igneous Formed when magma cools and solidifies.
  The type of texture is determined by the
  composition of the magma and the time it took to
  cool. Magma contains many different types of
  minerals in it that will solidify at different
  rates. Magma forms if either the pressure or
  temperature increases or the mineral composition
  changes.
• Glassy The magma was shock cooled (very
  rapid cooling) Ex. Obsidian
• Fine Grained The magma cooled quickly.
• Ex. Basalt
• Coarse Grained The magma took a long time
  to cool.
• Ex. Granite

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Igneous Rock Formations

• Intrusive Igneous Rock Formed when magma cools
  under the surface. The grains are large (coarse)
  because the upper rocks insulate the magma.
• Extrusive Igneous Rock Formed when lava cools
  and solidifies on the surface. They usually are
  formed in or around volcanoes and are fine
  grained or glassy (no crystals)
• Activity Draw the intrusive igneous bodies on p.
  100 of your book for bonus points.

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Sedimentary Rock

• Formed by the cementing of sediments that was
  laid down in layers.
• Strata Layers of sedimentary rock. This makes
  it easy to identify sedimentary rock.
• The classification of sedimentary rock is based
  on the way the rock was formed
• A. Clastic Fragments of rock cemented
  together.
• Ex. Conglomerate (Coarse Grained).
• B. Chemical Formed from solutions of
  dissolved minerals water.
  
• Ex. Halite (salt).
• C. Organic Formed from the remains of living
  organisms.
• Exs. Coral (tiny sea animals), Limestone
  (skeletal remains of sea animals) Coal
  (partially decomposed plant matter).

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Sedimentary Rock Structures

• Stratification The layering of sedimentary
  rocks.
• Ripple Marks The preserved movement of wind or
  waves in sedimentary rock.
• Mud Cracks Sediments that were exposed to the
  air and dried out indicating the location of
  ancient lake beds.

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Metamorphic Rock

• Metamorphic means changed shape. These are
  rocks in which the structure, texture or
  composition has been changed. Metamorphic change
  occurs when the temperature or pressure or both
  have changed.
• A. Contact Metamorphism Occurs when the
  magma is close by the rock formation and heats
  the surrounding rocks. This usually is limited to
  a small area.
• B. Regional Metamorphism Occurs when
  pressure builds up deep within the Earth or large
  pieces of crust collide. This occurs over a very
  large area.

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Composition of Metamorphic Rock

• When temperature and pressure change, the
  minerals within a rock will change to a more
  stable mineral structure.
• Index Minerals Certain metamorphic rocks that
  are used to estimate the temperature, depth or
  pressure at which the rock went through
  metamorphism.
• Textures of metamorphic rocks under heat and
  pressure, the mineral grains are rearranged and a
  metamorphic rock can be changed into another type
  of metamorphic rock.
• A. Foliated The grains are arranged in
  bands.
• Ex. Shale turns into Slate.

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Composition of Metamorphic Rocks (cont.)

• B. Unfoliated The grains are NOT arranged
  in bands. These are usually made up of only one
  or two minerals.
• Recrystallization Occurs when the minerals
  change in size or composition and change the type
  of metamorphic rock.
• Deformation A change in the shape of a rock due
  to the force placed on causing it to squeeze or
  stretch and may create folds or bends in the rock
  layers.