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Chapter 5: Igneous Rocks

Chapter 5: Igneous Rocks. BIG Idea. Igneous rocks were the first rocks to form as Earth cooled from a molten mass to the crystalline rocks of the early crust. The word ‘Igneous’ means:. of or like fire [Latin ignis fire]. What are igneous rocks?. IGNEOUS rocks are….

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Chapter 5: Igneous Rocks

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  1. Chapter 5: Igneous Rocks

  2. BIGIdea Igneous rocks were the first rocks to form as Earth cooled from a molten mass to the crystalline rocks of the early crust.

  3. The word ‘Igneous’ means: • of or like fire [Latin ignis fire]

  4. What are igneous rocks?

  5. IGNEOUS rocks are… rocks that form when molten material cools and hardens either below or on Earth’s surface.

  6. How do we define MOLTEN? melted changed into liquid form by heat glowing ‘red-hot’

  7. MAGMA: THE PARENT TO ALL ROCKS Molten rock beneath the surface of the Earth (forms underground)

  8. LAVA: molten rock that flows out ON to Earth’s surface

  9. Igneous rocks are classified based on: mineral composition crystal size texture

  10. EXTRUSIVE: RAPID(fast) COOLING LAVA ON THE EARTH’S SURFACE small or no crystals fine-grained or glassy textures INTRUSIVE: SLOWCOOLING MAGMA DEEP WITHIN THE EARTH’S CRUST larger crystals coarser texture Two (2) Types of Igneous Rocks:

  11. TEXTURE • What is the ‘texture’ of an igneous rock? • the size, shape, and arrangement of the crystals

  12. 1. EXTRUSIVE:SMALL (or no) CRYSTALS - FINE GRAIN (fast cooling, no time to grow)

  13. EXTRUSIVErockscan have air pockets due to fast cooling… Can you name this rock? Hints: it’s the only rock that will float on water, and it’s used for pedicures…

  14. Pumice!

  15. This texture is described as ‘vesicular’ Gas pockets (holes) make the rock look ‘spongy’ pumice vesicular basalt

  16. scoria

  17. Also known as ‘volcanic glass’ Obsidian: cooled too quickly for crystals to form

  18. 2. INTRUSIVE:LARGE WELL-DEVELOPED CRYSTALS = COARSE GRAIN TEXTURE (slow cooling, a lot of time to grow)

  19. PORPHYRITIC: LARGE AND SMALL CRYSTALS Magma cooled in two stages

  20. 1.FELSIC: high silica (Si and O) and aluminum (Al) content light color low density COMPOSITION OF IGNEOUS ROCKS Rhyolite

  21. 2.MAFIC: high iron (Fe) and magnesium (Mg) content dark color high density Basalt

  22. 3. INTERMEDIATE: medium color medium density Diorite

  23. Lava Plateaus

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