Igneous RocksObjective: Understanding the different

ways igneous rocks form and their characteristics and locations.

Minerals IN Rocks Monominerallic

› 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

Rock Classification

Three Groups› Igneous: from fire› Sedimentary› Metamorphic

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

Magma vs. Lava

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Classification of Igneous Rocks

Classification – texture and composition

Igneous Textures

Coarse Grained› Slow cooling;

thousands to millions of years

› large crystals› Intrusive: below

ground› Minerals can be seen

with the naked eye

Igneous Textures

Fine Grained› Fast cooling; days to

weeks› Small crystals› Extrusive: above

ground› Ex: rhyolite

Igneous Textures

Glassy› No crystals; hours to days› Ex. obsidian

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

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

Igneous Rock Identification

Granitic/Felsic Igneous Rocks› high in aluminum› Light in color› Low density› Continental crust

Igneous Rock Identification

Basaltic/Mafic Igneous Rocks› High in iron and magnesium› Dark in color› High density› Oceanic crust

Igneous Rock Identification

Vesicular Igneous Rocks› Gas pockets› Cooled rapidly and gas could not escape› Example: Pumice

Igneous Rock Identification

Andesitic Rocks› Composed of both basaltic and granitic

rocks› Found in the Pacific Ocean and near

volcanoes

Continental vs. Oceanic

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

Continental vs. Oceanic

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