Classifying Rocks

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Chapter 5-1

• Classifying Rocks

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How Geologists Classify Rocks

• Rocks form mountains, hills, valleys, beaches and
  ocean floor
• Geologists observe the rocks color and texture
  and determine its mineral composition

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Texture

• Color alone does not provide enough information
• Texture the look and feel of the rocks surface
  (smooth or glassy)
• Grains made up of particles of minerals or
  other rocks
• Based upon size, shape, and pattern of grain
  rocks texture

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Grain

• Grain Size
• Coarse-grained (large enough to see)
• Fine-grained (so small need a microscope)
• Grain Shape
• Fine sand, small seeds, exploding stars, etc.
• Grain Pattern
• Flat layers (stack of pancakes), wavy, swirling
  patterns, rows, occur randomly
• No Visible Grain
• No grain.example flint

5
Mineral Composition

• Use microscope to identify minerals rock contains
• Cut rock very thin, so light can shine through
  its crystals

6
Origin

• Three major groups of rocks
• Igneous rock
• Forms from the cooling of molten rock (magma
  below surface or lava at the surface)
• Sedimentary rock
• Forms when particles of other rock or the remains
  of plants and animals are pressed and cemented
  together (layers below the surface)
• Metamorphic rock
• Formed when an existing rock is changed by heat,
  pressure, or chemical reactions (deep underground)