Igneous Rock Notes

Igneous rock forms when magma cools and solidifies. Formation

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) Classification

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

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

Gabbro Basalt Mafic Composition 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 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 Intrusive Texture

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

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

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