Chapter 7. Igneous Rocks

Adapted by Karla Panchuk from Physical Geology by Steven Earle

Figure 7.1 Lava lake of Mount Nyiragongo, a volcano in the Democratic Republic of Congo. Igneous rocks form when melted rock freezes. Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Photo by Baron Reznik (2015) CC BY-NC-SA 2.0 view source. Click the image for more attributions.

Learning Objectives

After reading this chapter and answering the review questions at the end, you should be able to:

  • Explain partial melting and the geological processes that lead to melting.
  • Describe the range of chemical compositions of magmas.
  • Discuss the processes that take place during magma cooling, and the order of crystallization in Bowen’s reaction series.
  • Explain how fractional crystallization and partial melting alter magma composition.
  • Classify igneous rocks according to the proportions of minerals within them.
  • Describe the origins of aphanitic, phaneritic, and porphyritic textures
  • Classify plutons according to their shapes and relationships to surrounding rocks.
  • Explain how chilled margins form.