Igneous RocksIgneous RocksChap. 5Chap. 5Chap. 5Chap. 5

• What are igneous rocks?• Identifying igneous rocks

What are igneous rocks? – 5.1

ObjectivesObjectives

• compare and contrast intrusive and extrusive rocks• describe the composition of magma• discuss the factors that affect how rocks melt and crystallize

Rhyolite breccia

I.I. DefinitionDefinition

Igneous Rocks Igneous Rocks

Rocks formed when magma crystallizes.Rocks formed when magma crystallizes.

‘‘Ignis’ = fireIgnis’ = fire

II.II.Types of Igneous rocksTypes of Igneous rocks

A.A. Extrusive – fine grained rocks that Extrusive – fine grained rocks that cool quickly, on Earth’s surfacecool quickly, on Earth’s surface

II.II.Types of Igneous rocksTypes of Igneous rocks

Basalt

B.B. Intrusive – Intrusive – -grained rocks -grained rocks that cool that cool , , the Earth the Earth

II.II.Types of Igneous rocksTypes of Igneous rocks

B.B. Intrusive – Intrusive – coarsecoarse-grained rocks -grained rocks that cool that cool slowlyslowly, , underunder the Earth the Earth

II.II.Types of Igneous rocksTypes of Igneous rocks

Granite

III.III. Magma compositionMagma composition

A.A. Molten rockMolten rock

III.III. Magma compositionMagma composition

A.A. Molten rockMolten rock

B.B. GasesGases

III.III. Magma compositionMagma composition

A.A. Molten rockMolten rock

B.B. GasesGases

C.C. Mineral crystalsMineral crystals

III.III. Magma compositionMagma composition

A.A. Molten rockMolten rock

B.B. GasesGases

C.C. Mineral crystalsMineral crystals

D.D. Magma ClassificationsMagma Classifications

III.III. Magma compositionMagma composition

A.A. Molten rockMolten rock

B.B. GasesGases

C.C. Mineral crystalsMineral crystals

D.D. Magma ClassificationsMagma Classifications

III.III. Magma compositionMagma composition

1.1. Basaltic – 50% SiOBasaltic – 50% SiO22

A.A. Molten rockMolten rock

B.B. GasesGases

C.C. Mineral crystalsMineral crystals

D.D. Magma ClassificationsMagma Classifications

III.III. Magma compositionMagma composition

1.1. Basaltic – 50% SiOBasaltic – 50% SiO22

2.2. Andesitic – 60% SiOAndesitic – 60% SiO22

A.A. Molten rockMolten rock

B.B. GasesGases

C.C. Mineral crystalsMineral crystals

D.D. Magma ClassificationsMagma Classifications

III.III. Magma compositionMagma composition

1.1. Basaltic – 50% SiOBasaltic – 50% SiO22

2.2. Andesitic – 60% SiOAndesitic – 60% SiO22

3.3. Rhyolitic – 70% SiORhyolitic – 70% SiO22

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

A.A. Temperature Temperature (increases with (increases with depth)depth)

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

A.A. Temperature (increases with depth)Temperature (increases with depth)

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

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

A.A. Temperature (increases with depth)Temperature (increases with depth)

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

C.C. HH22O content (more HO content (more H22O, melting pt. O, melting pt. ↓)↓)

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

A.A. Temperature (increases with depth)Temperature (increases with depth)

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

C.C. HH22O content (more HO content (more H22O, melting pt. O, melting pt. ↓)↓)

D.D. Mineral contentMineral content

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

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

A.A. Temperature (increases with depth)Temperature (increases with depth)

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

C.C. HH22O content (more HO content (more H22O, melting pt. O, melting pt. ↓)↓)

D.D. Mineral contentMineral content

IV.IV. Magma Formation is Magma Formation is Influenced byInfluenced by

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

V.V. Melting RocksMelting Rocks

A.A. Partial meltingPartial melting

V.V. Melting RocksMelting Rocks

Some minerals melt while others remain solidSome minerals melt while others remain solid

A.A. Partial meltingPartial melting

V.V. Melting RocksMelting Rocks

Some minerals melt while others remain solidSome minerals melt while others remain solid

HEAT

A.A. Partial meltingPartial melting

B.B. Fractional crystallizationFractional crystallization

V.V. Melting RocksMelting Rocks

As liquid rock cools certain minerals crystallize As liquid rock cools certain minerals crystallize before othersbefore others

A.A. Partial meltingPartial melting

B.B. Fractional crystallizationFractional crystallization

V.V. Melting RocksMelting Rocks

As liquid rock cools certain minerals crystallize As liquid rock cools certain minerals crystallize before othersbefore others

COOLING

A chart that shows how minerals crystallize A chart that shows how minerals crystallize when cooledwhen cooled

VI.VI. Bowen’s SeriesBowen’s Series

A.A. Two pathsTwo paths

VI.VI. Bowen’s SeriesBowen’s Series

A.A. Two pathsTwo paths

VI.VI. Bowen’s SeriesBowen’s Series

1.1. Continuous path for feldsparsContinuous path for feldspars

A.A. Two pathsTwo paths

VI.VI. Bowen’s SeriesBowen’s Series

1.1. Continuous path for feldsparsContinuous path for feldspars

2.2. Stepwise path for Fe/Mg mineralsStepwise path for Fe/Mg minerals

A.A. Two pathsTwo paths

B.B. Both paths end with Si and O – the Both paths end with Si and O – the last minerals to crystallizelast minerals to crystallize

VI.VI. Bowen’s SeriesBowen’s Series

VI.VI. IntrusionsIntrusions

A.A. Quartz (SiOQuartz (SiO22) finds way into rock ) finds way into rock veinsveins

VI.VI. IntrusionsIntrusions

Quartz vein

A.A. Quartz (SiOQuartz (SiO22) finds way into rock ) finds way into rock veinsveins

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

VI.VI. IntrusionsIntrusions

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Classifying Igneous Rocks 5.2

ObjectivesObjectives• Classify different types and textures of igneous rocks• Recognize the effects of cooling rates on the grain sizes• Describe some uses of igneous rocks

Basalt

I.I. Where rock formsWhere rock forms

I.I. Where rock formsWhere rock formsA.A. Intrusive forms Intrusive forms ..

I.I. Where rock formsWhere rock formsA.A. Intrusive forms Intrusive forms under surfaceunder surface..

B.B. Extrusive forms Extrusive forms ..

I.I. Where rock formsWhere rock formsA.A. Intrusive forms Intrusive forms under surfaceunder surface..

B.B. Extrusive forms Extrusive forms above surfaceabove surface..

II.II. Rock’s compositionRock’s composition

II.II. Rock’s compositionRock’s compositionA.A. Felsic – silicon-rich, light coloredFelsic – silicon-rich, light colored

Granite

II.II. Rock’s compositionRock’s compositionA.A. Felsic – silicon-rich, light coloredFelsic – silicon-rich, light colored

B.B. Mafic – iron & magnesium rich, Mafic – iron & magnesium rich, dark coloreddark colored

Gabbro

II.II. Rock’s compositionRock’s compositionA.A. Felsic – silicon-rich, light coloredFelsic – silicon-rich, light colored

B.B. Mafic – iron & magnesium rich, Mafic – iron & magnesium rich, dark coloreddark colored

C.C. Ultramafic – very high levels of Fe Ultramafic – very high levels of Fe & Mg& Mg

Peridotite

III.III. TextureTextureA.A. Phaneritic has coarse grainsPhaneritic has coarse grains

Granite

III.III. TextureTextureB.B. Aphanitic is fine-grainedAphanitic is fine-grained

Basalt

III.III. TextureTextureC.C. Vessicular – has tiny holesVessicular – has tiny holes

Vessicular Basalt

III.III. TextureTextureD.D. Glassy – has no visible grainsGlassy – has no visible grains

Obsidian

III.III. TextureTextureE.E. Porphyritic – has Porphyritic – has large grainslarge grains

surrounded by surrounded by smaller grainssmaller grains

Andesite

IV.IV. Igneous rocks as resourcesIgneous rocks as resources

IV.IV. Igneous rocks as resourcesIgneous rocks as resourcesA.A. They are strong and resist They are strong and resist

weatheringweathering

A.A. They are strong and resist They are strong and resist weatheringweathering

B.B. Granite is a common construction Granite is a common construction materialmaterial

IV.IV. Igneous rocks as resourcesIgneous rocks as resources

V.V. Ores Ores

Minerals that contain useful substances that Minerals that contain useful substances that are mined for profitare mined for profit

A.A. Important metallic elements often Important metallic elements often found near veinsfound near veins

V.V. Ores Ores

A.A. Important metallic elements often Important metallic elements often found near veinsfound near veins

B.B. PegmatitesPegmatites

V.V. Ores Ores

Veins of extremely large-grained mineralsVeins of extremely large-grained minerals

A.A. Important metallic elements often Important metallic elements often found near veinsfound near veins

B.B. PegmatitesPegmatites

C.C. KimberlitesKimberlites

V.V. Ores Ores

These contain diamondsThese contain diamonds

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