Download Igneous Rocks…

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Vocabulary
 Magma
 Molten rock
beneath Earth’s
surface
 Lava
 Molten rock that
reaches Earth’s
surface through a
volcano
Igneous Rocks…
Formation
Cooling
Time
Crystal
Size
Mineral
Composition
Color
Origin
Igneous Rocks are classified on
what minerals make up the rock
and the size of mineral crystals.
Origin of Igneous Rocks
Igneous rocks are classified as INTRUSIVE or EXTRUSIVE

Intrusive
 Forms when
magma cools within
Earth
 Magma cools slowly
being exposed to
high temperatures
 Reach surface
when forces inside
Earth push rocks up
& wind and water
break apart/carry
away surface rocks

Extrusive
 Forms when lava
cools on Earth’s
surface
 Lava cools quickly
being exposed to
cool temperatures
 Reach surface
through volcanoes
erupting
Intrusive Igneous Rocks
Forms from magma within Earth’s surface
Granite
Peridotite
Diorite
Anorthosite
Gabbro
Pegmatite
Extrusive Igneous Rocks
Forms from lava on Earth’s surface
Basalt
Rhyolite
Pumice
Andesite
Obsidian
Scoria
Textures of Igneous Rocks
Texture of an igneous rock is determined by the size of its
mineral crystals.
Size of mineral crystals depends on
how quickly the magma or lava cools.
Textures of Igneous Rocks
 Intrusive
 Interior of Earth is
HOT
 Extrusive
 Surface of Earth is
COOL
 High Temperatures
 Lower temperatures
allow magma to
cool SLOWLY
cause the lava to
cool QUICKLY
 Slow cooling allows
time for LARGE
mineral crystals to
form
 No time for large
mineral crystals to
form so there are
SMALL mineral
crystals
Composition of Igneous Rocks
Texture is not enough to identify an Igneous Rock. Some
Igneous Rocks have similar textures. Composition is based
on Silicate levels.

Silica: Compound made up of silicon and oxygen which
geologists use to classify rocks
Estimate SILICATE level by COLOR

LIGHT COLOR
HIGH LEVELS OF SILICA
Granite/Rhyolite
Gabbro/Basalt

LOW LEVELS OF SILICA
DARK COLOR
Rocks in the World Around Us
Rocks in the World Around Us