
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

Three Groups
› Igneous: from fire
› Sedimentary
› Metamorphic

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
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
Classification – texture and composition

Coarse Grained
› Slow cooling; thousands
to millions of years
› large crystals
› Intrusive: below ground
› Minerals can be seen
with the naked eye

Fine Grained
› Fast cooling; days to
weeks
› Small crystals
› Extrusive: above
ground
› Ex: rhyolite

Glassy
› No crystals; hours to days
› Ex. obsidian

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

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

Granitic/Felsic Igneous Rocks
› high in aluminum
› Light in color
› Low density
› Continental crust

Basaltic/Mafic Igneous Rocks
› High in iron and magnesium
› Dark in color
› High density
› Oceanic crust

Vesicular Igneous Rocks
› Gas pockets
› Cooled rapidly and gas could not escape
› Example: Pumice

Andesitic Rocks
› Composed of both basaltic and granitic
rocks
› Found in the Pacific Ocean and near
volcanoes

Continental Igneous Rocks
› Composition: silicon and aluminum
› Density: low
› Thickness: very thick
› Example: granite, light in color, felsic

Oceanic Igneous Rocks
› Composition: silicon, iron, magnesium
› Density: high
› Thickness: very thin
› Example: basalt, dark in color, mafic