chapter 5: igneous rocks
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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…. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 5: Igneous Rocks
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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.
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The word ‘Igneous’ means:
of or like fire [Latin ignis fire]
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What are igneous rocks?
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IGNEOUS rocks are…rocks that form when molten material cools and hardens either below or on Earth’s surface.
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How do we define MOLTEN?
melted changed into liquid form by
heat glowing ‘red-hot’
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MAGMA: THE PARENT TO ALL ROCKS
Molten rock beneath the surface of the Earth (forms underground)
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LAVA: molten rock that flows out ON to Earth’s surface
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Igneous rocks are classified based on:
1. mineral composition2. crystal size3. texture
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Two (2) Types of Igneous Rocks:
1. EXTRUSIVE: RAPID (fast) COOLING LAVA ON THE EARTH’S SURFACE
small or no crystals fine-grained or glassy textures
2. INTRUSIVE: SLOW COOLING MAGMA DEEP WITHIN THE EARTH’S CRUST
larger crystals coarser texture
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TEXTURE What is the ‘texture’ of an igneous rock?
the size, shape, and arrangement of the crystals
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1. EXTRUSIVE: SMALL (or no) CRYSTALS - FINE GRAIN (fast
cooling, no time to grow)
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EXTRUSIVE rocks can 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…
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Pumice!
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This texture is described as ‘vesicular’
Gas pockets (holes) make the rock look ‘spongy’
pumice vesicular
basalt
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scoria
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Obsidian: cooled too quickly for crystals to form
Also known as ‘volcanic glass’
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2. INTRUSIVE: LARGE WELL-DEVELOPED CRYSTALS = COARSE GRAIN TEXTURE (slow cooling, a lot of time to grow)
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PORPHYRITIC: LARGE AND SMALL CRYSTALS
Magma cooled in two stages
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COMPOSITION OF IGNEOUS ROCKS
1. FELSIC: high silica (Si
and O) and aluminum (Al) content
light color low density
Rhyolite
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2. MAFIC: high iron (Fe)
and magnesium (Mg) content
dark color high density
Basalt
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3. INTERMEDIATE: medium color medium
density
Diorite
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Lava Plateaus