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Igneous Rocks. Chap. 5. What are igneous rocks? Identifying igneous rocks. Objectives. What are igneous rocks? – 5.1. compare and contrast intrusive and extrusive rocks describe the composition of magma discuss the factors that affect how rocks melt and crystallize. Rhyolite breccia.

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Igneous rocks

Igneous Rocks

Chap. 5

  • What are igneous rocks?

  • Identifying igneous rocks


What are igneous rocks 5 1

Objectives

What are igneous rocks? – 5.1

  • compare and contrast intrusive and extrusive rocks

  • describe the composition of magma

  • discuss the factors that affect how rocks melt and crystallize

Rhyolite breccia



Igneous Rocks

Rocks formed when magma crystallizes.

‘Ignis’ = fire



  • Extrusive – fine grained rocks that cool quickly, on Earth’s surface

Basalt


  • Intrusive – -grained rocks that cool , the Earth


  • Intrusive – coarse-grained rocks that cool slowly, under the Earth

Granite



  • Molten rock


  • Molten rock

  • Gases


  • Molten rock

  • Gases

  • Mineral crystals


  • Molten rock

  • Gases

  • Mineral crystals

  • Magma Classifications


  • Molten rock

  • Gases

  • Mineral crystals

  • Magma Classifications

  • Basaltic – 50% SiO2


  • Molten rock

  • Gases

  • Mineral crystals

  • Magma Classifications

  • Basaltic – 50% SiO2

  • Andesitic – 60% SiO2


  • Molten rock

  • Gases

  • Mineral crystals

  • Magma Classifications

  • Basaltic – 50% SiO2

  • Andesitic – 60% SiO2

  • Rhyolitic – 70% SiO2



  • Temperature (increases with depth)


  • Temperature (increases with depth)

  • Pressure (as pressure ↑, melting pt. ↑)


  • Temperature (increases with depth)

  • Pressure (as pressure ↑, melting pt. ↑)

  • H2O content (more H2O, melting pt. ↓)


  • Temperature (increases with depth)

  • Pressure (as pressure ↑, melting pt. ↑)

  • H2O content (more H2O, melting pt. ↓)

  • Mineral content

Granite has higher water content so it melts at a temperature


  • Temperature (increases with depth)

  • Pressure (as pressure ↑, melting pt. ↑)

  • H2O content (more H2O, melting pt. ↓)

  • Mineral content

Granite has higher water content so it melts at a lower temperature



  • Partial melting

Some minerals melt while others remain solid


  • Partial melting

HEAT

Some minerals melt while others remain solid


  • Partial melting

  • Fractional crystallization

As liquid rock cools certain minerals crystallize before others


  • Partial melting

  • Fractional crystallization

COOLING

As liquid rock cools certain minerals crystallize before others


A chart that shows how minerals crystallize when cooled



  • Two paths

  • Continuous path for feldspars


  • Two paths

  • Continuous path for feldspars

  • Stepwise path for Fe/Mg minerals


  • Two paths

  • Both paths end with Si and O – the last minerals to crystallize



  • Quartz (SiO2) finds way into rock veins

Quartz vein


  • Quartz (SiO2) finds way into rock veins

  • Intruded masses of rock cool in layers, often carrying metals (gold, silver, and platinum)



Classifying igneous rocks 5 2

Objectives

Classifying Igneous Rocks 5.2

Basalt

  • Classify different types and textures of igneous rocks

  • Recognize the effects of cooling rates on the grain sizes

  • Describe some uses of igneous rocks



  • Intrusive forms .


  • Intrusive forms under surface.

  • Extrusive forms .


  • Intrusive forms under surface.

  • Extrusive forms above surface.



  • Felsic – silicon-rich, light colored

Granite


  • Felsic – silicon-rich, light colored

  • Mafic – iron & magnesium rich, dark colored

Gabbro


  • Felsic – silicon-rich, light colored

  • Mafic – iron & magnesium rich, dark colored

  • Ultramafic – very high levels of Fe & Mg

Peridotite


  • Phaneritic has coarse grains

Granite


  • Aphanitic is fine-grained

Basalt


  • Vessicular – has tiny holes

Vessicular Basalt


  • Glassy – has no visible grains

Obsidian


  • Porphyritic – has large grains surrounded by smaller grains

Andesite



  • They are strong and resist weathering


  • They are strong and resist weathering

  • Granite is a common construction material


Minerals that contain useful substances that are mined for profit


  • Important metallic elements often found near veins


  • Important metallic elements often found near veins

  • Pegmatites

Veins of extremely large-grained minerals


  • Important metallic elements often found near veins

  • Pegmatites

  • Kimberlites

These contain diamonds



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