Geology 101 - Lecture 6

Igneous Rocks

A. Definitions and Questions

• What is a magma?
• What is a magma chamber?
• Why do magmas rise to the surface?
• Why do magmas crystallize?
• Is the Earth the only planet that has volcanoes?

B. Classifications of Igneous Rocks

• Based on texture, chemical composition, and mineralogy
  • Difference between intrusive and extrusive rock (phaneritic vs. aphanitic)
  • Difference between felsic (=silicic) and mafic rocks
  • Relative percentage of ferromagnesian (dark) and light-colored minerals
  
  
• See Table 3.1 and Fig. 3.11 in your text
  • Basalt/Gabbro
  • Andesite/Diorite
  • Rhyolite/Granite

C. Bowen's Reaction Series

• A means to determine what minerals will crystallize at what temperature, and which minerals are typical in particular rock types. For example, olivine crystallizes from mafic magmas at high temperatures, thus you wouldn't expect to find it in a granite or a rhyolite (but you can find it in a basalt or a gabbro). Don't get bogged down in the details, just understand the basics of the Reaction Series

D. What are people who study Igneous Rocks called?

• Igneous Petrologists

E. What do Petrologists do?

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