The Rock Cycle

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The Rock Cycle
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The Rock Cycle

• Through many different geologic processes, the
  rocks that make up the earths crust form,
  change, get destroyed, and re-form over and over
  again. This is why it is called the rock CYCLE.
• There are constructive forces and destructive
  forces that drive the cycle.

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The Beginning

• Find magma on your rock cycle diagram.
• ALL rocks start as magma, thus the rock cycle
  begins in the earths interior where magma is
  still in the liquid state.
• It is placed at the bottom of this diagram
  because magma is found underground.
• Will not always be at the bottom of all rock
  cycle diagrams!

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The First Process

• As magma reaches the crust it is exposed to
  cooler temperatures and will harden.
• This is called crystallization
• Once crystallization has occurred, the magma is
  hard as a rock.
• This is a constructive force of nature.

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Igneous Rock

• Rocks that are formed directly from cooled magma
  are classified as igneous rocks.
• If the magma crystallized on the surface of the
  crust (on land), it is called extrusive igneous
  rock.
• If the magma crystallized while still in the
  crust (underground), it is called intrusive
  igneous rock.

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Examples

• Some examples of igneous rocks are
• Intrusive
• Granite, gabbro, quartz (also a mineral)
• Can usually see crystals or specks in the rock
  and mutlicolored
• Extrusive
• Basalt, obsidian, scoria (lava rock)
• Usually one color without visible crystals,
  sometimes have many holes or porous

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Next Process

• Once igneous rocks are formed they become exposed
  to the elements on the surface of earth.
• wind, rain, temperature changes, sun exposure
• This exposure causes
• Weathering breaking into pieces
• Erosion being moved (washed / blown away) to
  another location

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Lots and Lots of Little Pieces

• Once the destructive forces of weathering and
  erosion have occurred, sediments are formed.
• Dirt or soil, sand, silt, mud are all examples of
  sediments that have piled up after erosion
• Plants would not survive without this part of the
  rock cycle! No plants no animals!

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The Third Process

• Sediments pile up in low areas after erosional
  forces have slowed or stopped. This is called
  deposition.
• As deposition continues, layers of sediments
  continue to pile up, and they compact the layers
  on the bottom. This is called compaction.
• Once compaction occurs, the sediments begin to
  glue together which is called cementation.
  (like the word cement)

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Third Process Continued

• These constructive forces of
• Deposition
• Compaction
• Cementation
• are all steps in what is called lithification-
  the process of loose sediments turning into rock.
• Once sediments lithify, new rock forms

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Sedimentary Rocks

• After lithification of the sediments, the rocks
  that are formed are classified as sedimentary
  rocks.
• Sedimentary rocks are the only type of rock that
  fossils are found in because of the way they
  form.

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Examples

• Sedimentary Rocks are often coarse in texture and
  have layers, and or visible grains
• Common sedimentary rocks are
• Sandstone
• Chert (flint rock)
• Conglomerate
• Limestone
• Shale

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The Fourth Process

• Because of the way sedimentary rocks form, they
  usually get pushed further and further down into
  the crust from sediments continuing to layer on
  top.
• The deeper the sedimentary rocks get in the
  crust, they are exposed to increasing heat and
  pressure.

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Fourth Process Continued

• This increase in heat pressure changes the
  rock, a lot like pressing 2 colors of playdough
  togethertheyll eventually mix colors.
• This change in the rock due to high heat and
  pressure is called metamorphism, (both a
  destructive and constructive force) and a new
  type of rock is formed.

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Metamorphic Rock

• The process of metamorphism creates the rocks
  classified as metamorphic rocks.
• Only occurs deep in the crust or near volcanoes
  where there is high enough temperatures and
  pressure. Therefore most metamorphic rock is
  found deep underground or near volcano sites.

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Examples

• All metamorphic rocks have a parent rock, or
  the original igneous or sedimentary rock it came
  from.
• Common metamorphic rocks
• Slate (parent rock Shale)
• Marble (parent rock Limestone)
• Gneiss (parent rock Granite)

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Last Process

• If metamorphic rocks remain deep underground they
  eventually get pushed so far down that they begin
  melting back into the magma.
• This last destructive force completes the rock
  cycle.
• The whole thing can then start all over!

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Loops within the Rock Cycle

• If an igneous rock remains underground, it will
  go through metamorphism and turn into metamorphic
  rock.
• If sedimentary or metamorphic rocks are exposed
  to the surface of the crust, they will experience
  weathering and erosion and turn into sediments.

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