21.3 Rocks and the Rock Cycle

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21.3 Rocks and the Rock Cycle

• Rocks are classified into three major groups
  based on how they formed
• Igneous Rocks
• Can be divided into two categories based on where
  they form

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• A. Intrusive Rocks igneous rocks that form
  underground from magma
• Cool slowly allowing crystals to grow large
  giving it a coarse-grain texture

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• B. Extrusive Rocks igneous rocks that form at
  the surface from lava
• Cool quickly resulting in the crystals to be
  small giving it a fine grain texture

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Igneous Rock Textures

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• II. Sedimentary Rock rock that forms over time
  as sediment is squeezed and cemented together
• Sediment small, solid pieces of material that
  comes from rocks or living organisms
• Sediment is deposited in layers by running water
  or wind
• Sediment is cemented together by pressure from
  overlying layers
• Three Main Groups of Sedimentary Rocks
• 1. Clastic
• 2. Chemical
• 3. Organic

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• Clastic Rock sedimentary rocks that form from
  the broken fragments of other rocks
• Clastic Rocks are classified based on the size of
  their fragments
• Example Conglomerate rock fragments that
  consist of gravel and pebbles

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• Some clastic rocks are made of smaller particles
  (sandstone)

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• 2. Chemical Rocks rocks that form when
  minerals precipitate out of solution
• Example when ocean water evaporates (halite)

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• Organic Rocks rocks that form as a result
  of organic processes
• Shells of marine animals like corals, clams,
  mussels sink to the ocean floor when they die.
• Example Limestone and calcite (chalk)

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• III. Metamorphic Rocks rock that have been
  changed by temperature, pressure, or chemical
  reactions.
• Most metamorphic rocks form under high
  temperatures and pressures deep underground.
  (slate and schist shown below)

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Metamorphic Rocks

• Foliation a layering of minerals in a rock due
  to intense pressure squeezing the crystals
  together.

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Metamorphic Rock pictures

• Metamorphic Rocks like gneiss show banding of
  light and dark minerals.

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Metamorphic Rocks and their Parent Rocks

• Examples
• Slate parent is shale
• Gneiss parent is granite/schist
• Quartzite parent is sandstone
• Marble parent is limestone

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IV. Rock Cycle

• Rock Cycle series of processes in which rocks
  continuously change from one type to another.