Igneous Rock Notes Formation Igneous rock forms when

Igneous Rock Notes

Formation • Igneous rock forms when magma cools and solidifies.

Classification • Igneous rocks are classified by texture and composition. • Texture • The sizes, shapes, and positions of the grains that a rock is made of • Composition – The minerals or elements that make up a rock

Classification • Composition • Felsic or Mafic • Texture – Fine-grained (extrusive) or coarse-grained (intrusive)

General Composition – The types of minerals found in an igneous rock (the composition) impact the color and density of the rock.

Granite Felsic Composition • Felsic – light colored, less dense Rhyolite – Rich in aluminum, potassium, silicon, and sodium.

Gabbro Mafic Composition Basalt • Mafic – dark colored, more dense – Rich in calcium, iron, and magnesium

Composition

Intrusive Texture • Intrusive Igneous Rock – Form inside Earth’s crust • Cool slowly – Coarse-grained (large particles)

Intrusive Texture • Intrusive Igneous Rock Formations – Batholiths: The largest of all igneous intrusions – Stocks: Intrusive bodies that are exposed over smaller areas than batholiths – Dikes: Sheet-like intrusions that cut across previous rock units – Laccolith: Sheet-like intrusions that run parallel to previous rock units – Volcanic neck: A column of igneous rock formed when magma hardens with in a vent

Extrusive Texture • Extrusive Igneous Rock – Form on Earth’s surface • Cool quickly – Fine-grained (small particles)

Extrusive Texture • Extrusive Igneous Rock Formations – Lava Flow: Formed when lava erupts from a volcano – Fissure: Long cracks in Earth’s crust where lava can flow

Igneous Rock Flow Chart rock melts pressure rock cools composition temperature igneous rock Slow cooling (coarse-grained) Fast cooling (fine -grained)