Igneous Rocks - Dynamic Earth - Lecture Slides, Slides of Earth Sciences

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Igneous Rocks

Igneous = fire

• Figure 4.

Magma

Man in

Action

Lava Man

taking a

break

General characteristics

of magma

 The nature of magma

• Consists of three components:
  • Liquid portion = melt
  • Solids, if any, are silicate minerals
  • Volatiles = dissolved gases in the melt, including water vapor (H 2 O), carbon dioxide (CO 2 ), and sulfur dioxide (SO 2 )

Igneous textures

 Texture is used to describe the overall

appearance of a rock based on the size,

shape, and arrangement of interlocking

minerals

 Factors affecting crystal size

• Rate of cooling
  • Slow rate = fewer but larger crystals
  • Fast rate = many small crystals
  • Very fast rate forms glass

Igneous textures

 Factors affecting crystal size

• % of silica (SiO 2 ) present
• Dissolved gases

Aphanitic texture

Figure 4.3 A

Phaneritic texture

Figure 4.3 B

Porphyritic texture

Figure 4.3 C

Glassy texture

Figure 4.3 D