Recap Qs: What are the two most abundant elements in crustal rocks

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Recap Qs What are the two most abundant
elements in crustal rocks?

• A. Potassum and Sodium
• B. Calsum and Aluminum
• C. Copper and Iron
• D. Silicon and Oxygen

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Recap Qs Why can mica be easily splitted into
thin sheets ?

• A. mica is a silicate mineral.
• B. mica is soft.
• C. mica has a sheet silicate structure.
• D. mica has a single-chain silicate structure.

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Principles of Geology

• Chapter 4 Igneous Rocks

Mian Liu 2007
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Igneous Rocks

• Name from latin ignis, or fire
• Formed from cooling and solidification
  (crystallization) of magma.

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General characteristics of magma

• General characteristic of magma
• Rocks formed from lava extrusive, or volcanic
  rocks
• Rocks formed from magma at depth intrusive, or
  plutonic rocks

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Classification of Igneous rocks

• Texture
• Mineral composition

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• Texture overall appearance of rocks based on
  size, shape, arrangement of their interlocking
  cystals.
• Reflect the environment in which the rocks formed.

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Factors contribute to the textures of igneous
rocks

• Magma cooling rate
• Amount of silica in the magma
• Amount of dissolved gas in the magma

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Igneous Textures

• Aphanitic (fine-grained)
• Phaneritic (coarse-grained)
• Pegmatic (exceptionally coarse grained)
• Porphyritic (phenocrysts goundmass)
• Glassy
• Pyroclastic (associated with volcanic eruption)

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Naming Igneous Rocks

• Texture
• Phaneritic (intrusive)
• Aphanitic (extrusive)
• Composition
• Ultramafic
• Mafic
• Intermediate
• Felsic

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Magma generation

• Increase temperature
• Reduce pressure
• Add water and other volatiles

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Temperature in Earths interior
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Pressure-release partial melting
Partial melting starts
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Assimilation, magma mixing, and magmatic
differentiation