Igneous Rocks Chap. 5 What are igneous rocks? Identifying igneous rocks

What are igneous rocks? – 5.1Objectives 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.Definition

Igneous Rocks Rocks formed when magma crystallizes. ‘Ignis’ = fire

II.Types of Igneous rocks

A.Extrusive – fine grained rocks that cool quickly, on Earth’s surface II.Types of Igneous rocks Basalt

B.Intrusive – -grained rocks that cool, the Earth II.Types of Igneous rocks

B.Intrusive – coarse-grained rocks that cool slowly, under the Earth II.Types of Igneous rocks Granite

III. Magma composition

A.Molten rock III. Magma composition

A.Molten rock B.Gases III. Magma composition

A.Molten rock B.Gases C.Mineral crystals III. Magma composition

A.Molten rock B.Gases C.Mineral crystals D.Magma Classifications III. Magma composition

A.Molten rock B.Gases C.Mineral crystals D.Magma Classifications III. Magma composition 1. Basaltic – 50% SiO 2

A.Molten rock B.Gases C.Mineral crystals D.Magma Classifications III. Magma composition 1. Basaltic – 50% SiO 2 2. Andesitic – 60% SiO 2

A.Molten rock B.Gases C.Mineral crystals D.Magma Classifications III. Magma composition 1. Basaltic – 50% SiO 2 2. Andesitic – 60% SiO 2 3. Rhyolitic – 70% SiO 2

IV. Magma Formation is Influenced by

A.Temperature (increases with depth) IV. Magma Formation is Influenced by

A.Temperature (increases with depth) B.Pressure (as pressure ↑, melting pt. ↑) IV. Magma Formation is Influenced by

A.Temperature (increases with depth) B.Pressure (as pressure ↑, melting pt. ↑) C.H 2 O content (more H 2 O, melting pt. ↓) IV. Magma Formation is Influenced by

A.Temperature (increases with depth) B.Pressure (as pressure ↑, melting pt. ↑) C.H 2 O content (more H 2 O, melting pt. ↓) D.Mineral content IV. Magma Formation is Influenced by Granite has higher water content so it melts at a temperature

A.Temperature (increases with depth) B.Pressure (as pressure ↑, melting pt. ↑) C.H 2 O content (more H 2 O, melting pt. ↓) D.Mineral content IV. Magma Formation is Influenced by Granite has higher water content so it melts at a lower temperature

V. Melting Rocks

A.Partial melting V. Melting Rocks Some minerals melt while others remain solid

A.Partial melting V. Melting Rocks Some minerals melt while others remain solid HEAT

A.Partial melting B.Fractional crystallization V. Melting Rocks As liquid rock cools certain minerals crystallize before others

A.Partial melting B.Fractional crystallization V. Melting Rocks As liquid rock cools certain minerals crystallize before others COOLING

A chart that shows how minerals crystallize when cooled VI. Bowen’s Series

A.Two paths VI. Bowen’s Series

A.Two paths VI. Bowen’s Series 1.Continuous path for feldspars

A.Two paths VI. Bowen’s Series 1.Continuous path for feldspars 2. Stepwise path for Fe/Mg minerals

A.Two paths B.Both paths end with Si and O – the last minerals to crystallize VI. Bowen’s Series

VI. Intrusions

A.Quartz (SiO 2 ) finds way into rock veins VI. Intrusions Quartz vein

A.Quartz (SiO 2 ) finds way into rock veins B.Intruded masses of rock cool in layers, often carrying metals (gold, silver, and platinum) VI. Intrusions

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Classifying Igneous Rocks 5.2 Objectives 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.Where rock forms

A.Intrusive forms.

I.Where rock forms A.Intrusive forms under surface. B.Extrusive forms.

I.Where rock forms A.Intrusive forms under surface. B.Extrusive forms above surface.

II. Rock’s composition

A.Felsic – silicon-rich, light colored Granite

II. Rock’s composition A.Felsic – silicon-rich, light colored B.Mafic – iron & magnesium rich, dark colored Gabbro

II. Rock’s composition A.Felsic – silicon-rich, light colored B.Mafic – iron & magnesium rich, dark colored C.Ultramafic – very high levels of Fe & Mg Peridotite

III. Texture A.Phaneritic has coarse grains Granite

III. Texture B.Aphanitic is fine-grained Basalt

III. Texture C.Vessicular – has tiny holes Vessicular Basalt

III. Texture D.Glassy – has no visible grains Obsidian

III. Texture E.Porphyritic – has large grains surrounded by smaller grains Andesite

IV. Igneous rocks as resources

A.They are strong and resist weathering

B.Granite is a common construction material IV. Igneous rocks as resources

V. Ores Minerals that contain useful substances that are mined for profit

A.Important metallic elements often found near veins V. Ores

A.Important metallic elements often found near veins B.Pegmatites V. Ores Veins of extremely large-grained minerals

A.Important metallic elements often found near veins B.Pegmatites C.Kimberlites V. Ores These contain diamonds

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