Igneous Rock Notes

Igneous rock forms when magma cools and

solidifies.

• Composition– Felisc or Mafic

• Texture– Intrusive or Extrusive

Classification

Classification

• Felsic – light colored, less dense– Rich in aluminum,

potassium, silicon, and sodium.

Granite

Rhyolite

Gabbro

Basalt

Classification

• Mafic – dark colored, more dense– Rich in calcium, iron, and

magnesium

Texture• Intrusive Igenous Rock – inside Earth’s crust

(corase-grained)

• Intrusive Igneous Rock Formations– Pluton: Large, irregular shaped intrusive

bodies– Batholiths: The largest of all igneous

intrusions– Stocks: Intrusive bodies that are exposed

over smaller areas than batholiths– Dikes: Sheetlike intrusions that cut across

previous rock units– Laccolith: Sheetlike intrusions that are

oriented parallel to previous rock units– Volcanic neck: A column of igneous rock

formed when magma hardens with in a vent

Texture

Texture• Extrusive Igenous Rock – on Earth’s surface

(fine-grained)

• Extrusive Igneous Rock Formations– Lava Flow: Formed when lava

erupts from a volcano– Fissure: Long cracks in Earth’s

crust where lava can flow

Texture

Igneous Rock Flow Chart

rock melts

rock cools

igneous rock

pressure

temperature

compositionSlow cooling (coarse-grained)

Fast cooling (fine-grained)