Ch. 4.2 Igneous Rocks
forms when
molten/melted rock
(magma or lava) cools
and hardens (solidifies)
Igneous Rocks
• ignis which means “fire”
• think of “ignite”
• probably first rocks on Earth
Label the lava and magma
Igneous rock--mineral composition
• Felsic
– forms light-colored
rocks
– less dense
– lots of aluminum,
potassium, silicon,
and sodium
– ex: granite
• Mafic
– forms darkcolored rocks
– lots of
calcium, iron,
and
magnesium
(low in silicon)
– ex: basalt
Two Types of igneous rocks
• 1. Intrusive
• 2. Extrusive
– from magma
– from lava (fine(coarse-grained)—
grained)—cool
cool slowly
quickly
– ex: granite
– ex: basalt
• most abundant
• most common
igneous rock
extrusive
• makes up much
igneous rock
of continental
• especially
crust
common in
• forms core of
oceanic crust
many mountain
ranges
Questions:
1. What is the most common igneous rock?
2. Why does PUMICE float in water?
3. Why does lava cool more quickly than
magma?
4. What determines the texture of an
igneous rock?
5. A batholith forms from a large magma
chamber that slowly cools deep beneath
the earth’s surface. What type of texture is
this igneous rock formation most likely to
have?