Classifying Rocks

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Classifying Rocks

• What characteristics are used to identify rocks?

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Color
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texture
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Texture Is

• The look and feel of the rocks surface

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Mineral Composition
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Check your understanding

• What three characteristics do geologists use to
  identify a rock sample?

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What is meant by the texture of a rock?
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Rock Groups

• There are three major groups of rocks

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Igneous Rocks
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Igneous Rock forms from the cooling of molten
rock either magma below the surface or lava at
the surface
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Geologists classify igneous rocks according to
where they formed

• Intrusive
• Formed from Magma
• Beneath the surface

• Extrusive
• Formed from Lava

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Sedimentary Rocks
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Sedimentary rock forms when particles of other
rocks or the remains of plants and animals are
pressed and cemented together.
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Sedimentary Rocks form in layers beneath the
earths surface. As the surface is weathered
away they are exposed.
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Geologists classify sedimentary rocks according
to the type of sediment that make up the rock.
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3 groups of Sedimentary Rocks

• 1. Clastic rock fragments squeeze
• together (shale Sandstone Breccia)

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2. Organic Sedimentary Rock

• Forms where the remains of plants and animals are
  deposited in thick layers.
• Coal
  and limestone

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3. Chemical Sedimentary Rock

• Forms when minerals that are dissolved in a
  solution crystallize. (chemical limestone)

• Chemical rocks can also form when seas or lakes
  evaporate, (Gypsum)

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Metamorphic Rock

• Formed when an existing rock is changed by heat,
  pressure or chemical reactions.

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Geologists classify Metamorphic Rocks by the
arrangement of the grains that make up the rock.

• Foliated
• arranged in parallel layers or bands
• Gneiss slate schist

• Non-foliated
• Mineral grains arranged randomly
• (do not split into layers)
• Marble quartzite

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Checking your understanding

• What are the three MAJOR ROCK Groups?

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How do Geologists classify Igneous Rocks?What
are the 2 types of igneous rocks?
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How do Geologists classify Sedimentary
Rocks?What are the 3 major groups of
Sedimentary Rocks?
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How do Geologists Classify Metamorphic
Rocks?What are the 2 major types of Metamorphic
Rocks?
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How do Igneous Rocks form?
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How do Sedimentary Rocks Form?
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How do Metamorphic Rocks Form?