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6.2 Igneous Rocks

Learn about felsic and mafic igneous rocks classified by magma movements, composition, and cooling processes. Explore examples like granite, gabbro, and diorite. Understand intrusive formations like dikes, sills, batholiths, and laccoliths.

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6.2 Igneous Rocks

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  1. 6.2 Igneous Rocks

  2. Igneous Rock Formation Igneous rocks are classified as: Felsic – Thick and slow moving magma. • Contains Silica, Ca, Fe and Mg • Forms light colored quartz and orthoclase feldspar

  3. Igneous Rock Formation Igneous rocks are classified as: Mafic: Formed from hotter, thinner and more fluid. • Contains large amounts of Fe, Mg and low amounts of silica. • Forms darker rocks.

  4. Igneous Rock Formation Underground Magma • Forms Intrusive Rocks • Cools slowly • Has coarse surfaces • Produces larger crystals within the rock.

  5. Igneous Rock Formation Magma Above the Surface (Lava) • Forms Extrusive Rocks • Cools Quickly • Forms Microscopic/no crystals • May form porphyry (large crystals surrounded by fine grained rock)

  6. Igneous Rock Formation Igneous Rock Description • Granite Family • Felsic • Coarse (Intrusive) • Makes up most of the continental crust • Only visible after upward expansion. • Other examples: Pumice and Obsidian

  7. Igneous Rock Formation Igneous Rock Description • Gabbro • Darker • Dense

  8. Igneous Rock Formation Igneous Rock Description • Diorite Family • Grays and greens • Coarse Grained

  9. Igneous Rock Formation Igneous Intrusion • What is an igneous intrusion? A rock mass that cools inside the Earth’s interior (Pluton). • These include: • Dikes – Vertically cooled igneous rock • Sills – Horizontally cooled igneous rock (b/t rock layers)

  10. Igneous Rock Formation Igneous Intrusions Batholiths • Largest plutons • Made of granite or granordiorite • The cores of many mountain ranges • Exposed through upward expansion Laccoliths • Magma that bulges upwards into domes

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