1. Igneous Rocks
Objective: Understanding the different ways igneous rocks form and their characteristics and locations.

2. Minerals IN Rocks Monominerallic Polyminerallic
Rocks made up of only one mineral
Ex. Rock Salt = Halite; Limestone = Calcite
Polyminerallic
Rocks made up of more than one mineral
Ex. Granite, Andesite

3. Rock Classification Three Groups Igneous: from fire Sedimentary
Metamorphic

4. Igneous Rocks Igneous Rock
Rocks formed from molten rock material that cools and solidifies
Magma: molten rock material below the Earth’s surface; forced upward towards the surface by density differences in the magma
Lava: molten rock material above the Earth’s surface

5. Magma vs. Lava
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6. Classification of Igneous Rocks
Classification – texture and composition

7. Igneous Textures Coarse Grained
Slow cooling; thousands to millions of years
large crystals
Intrusive: below ground
Minerals can be seen with the naked eye

8. Igneous Textures Fine Grained Fast cooling; days to weeks
Small crystals
Extrusive: above ground
Ex: rhyolite

9. Igneous Textures
Glassy
No crystals; hours to days
Ex. obsidian

10. Types of Igneous Rocks Intrusive Igneous Rocks
Formed inside the Earth from cooled magma
Pressure and temperature in the Earth are high, causing a slow rate of cooling
Slow cooling causes large crystals or a coarse texture
Example: Granite
Intrusion
Magma works its way up through rock layers as it cools

11. Types of Igneous Rocks Extrusive Igneous Rocks
Forms on the surface of the Earth from cooled lava
Rapid cooling causes small crystals (glassy texture or fine grained)
Example: Basalt
Extrusion
Lava makes its way down through rock layers as it cools

12. Igneous Rock Identification
Granitic/Felsic Igneous Rocks
high in aluminum
Light in color
Low density
Continental crust

13. Igneous Rock Identification
Basaltic/Mafic Igneous Rocks
High in iron and magnesium
Dark in color
High density
Oceanic crust

14. Igneous Rock Identification
Vesicular Igneous Rocks
Gas pockets
Cooled rapidly and gas could not escape
Example: Pumice

15. Igneous Rock Identification
Andesitic Rocks
Composed of both basaltic and granitic rocks
Found in the Pacific Ocean and near volcanoes

16. Continental vs. Oceanic
Continental Igneous Rocks
Composition: silicon and aluminum
Density: low
Thickness: very thick
Example: granite, light in color, felsic

17. Continental vs. Oceanic
Oceanic Igneous Rocks
Composition: silicon, iron, magnesium
Density: high
Thickness: very thin
Example: basalt, dark in color, mafic