ch. 6.2. igneous rocks. 1. intrusive igneous rock: formed from the cooling and solidification of...
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Ch. 6.2. Igneous Rocks
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1. Intrusive igneous rock: formed from the cooling and solidification of magma beneath Earth’s surface
2. Extrusive igneous rock: formed from the cooling and solidification of lava at Earth’s surface
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The Formation of Magma
• 3 factors influence rock melting:- temperature - pressure- presence of fluids in the rock (such as
water)
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Partial Melting• Minerals with lower melting points are the first
minerals to melt.
• As the temperature increases and as other minerals melt, the magma’s composition changes.
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The Formation of Magma
Chapter 6
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Fractional Crystallization
• Minerals that have the highest freezing points crystallize first.
• When magma cools, the cooling process is the reverse of the process of partial melting.
•
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The Formation of rocks
Chapter 6
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A. Intrusive Igneous Rock Structures
• Batholiths: intrusive formations that spread over a large area
• Stocks: similar to batholiths but smaller
• Sills: layers of rock parallel to the layers of rock that surround it.
• Dykes: new layers cutting across existing layers.
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B. Extrusive Igneous Rock Structures
– Volcano: a vent through which magma, gases, or volcanic ash is expelled.
– Lava flows, lava plateaus, and tuff layers
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Igneous RockIgneous Rock
MagmaMagma
MeltingMelting SolidifyingSolidifying
Partial MeltingPartial Melting Fractional Crystallization Fractional Crystallization
TextureTexture
IntrusiveIntrusive ExtrusiveExtrusive
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a. Coarse-Grained • Rocks cooled slowly, have large
mineral crystals
b. Fine-Grained • rocks cooled fast, have small grains.
Textures of Igneous Rocks:
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c. porphyritic texture: magma cooled slowly at first, but then cools more rapidly as the magma nears or reaches Earth’s surface– large crystals together with smaller
crystals.
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d. vesicular texture
– Contains bubbles of gases
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e. glassy texture: highly viscous magma cooled very rapidly
– No large crystals
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Composition of Igneous Rock
1. Felsic Rock: - rich in feldspars and silica- light in color.
• Ex: granite, rhyolite, obsidian, and pumice.
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2. Mafic Rock- rich in magnesium and iron,
dark in color.
• Example: basalt and gabbro.
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3. Intermediate Rocks: • proportions of silica between
felsic and mafic. • Examples: diorite and
andesite.
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Intrusive vs. extrusive igneous rock