Rocks

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Rocks
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James Hutton
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Modern Geology

• James Hutton found in 1795 a new concept
• Uniformitarianism
• The geologic process now at work were also active
  in the past
• The present physical features of Earth were
  formed by these same processes, at work over long
  periods of time

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Canyon or rivers formed how?

• According to Hutton, there need not be a sudden
  split in the Earths crust for this to happen,
• BUT
• It can be formed by the slow and steady wearing
  away of the land.

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Igneous rocks

• Rocks a group of minerals bound together in
  some way
• Igneous rock are formed by the cooling and
  hardening of hot molten rock from inside Earth.
  (magma)
• Sedimentary the hardening and cementing of
  layers of sediments
• Metamorphic rocks are formed when rocks that
  already exist are changed by heat and pressure
  into new kinds of rocks

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Recognizing Igneous Rocks

• Plutonic rocks that form underground from
  cooled magma are plutonic or intrusive
• Volcanic the rock that forms when lava cools is
  volcanic or extrusive.

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Rocks texture depends on?

• Size
• Shape
• Arrangement of the mineral crystal

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Igneous Rock textures

• Glassy smooth
• Obsidian
• Coarse-grained

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Porphyritic Texture

• When igneous rocks have large crystals that are
  surrounded by a fine-grained mass of rock.

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What effects crystal size

• The amount of time it takes for the magma to cool
• The amount of gas dissolved in the magma
• (sometimes the magma cools so fast that there
  is no time for crystals to form)